Gunsmithing the
AR-15 THE BENCH MANUAL

PATRICK SWEENEY

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TABLE OF CONTENTS

Special Offers

1 Background

2 Barrels

3 Iron Sights

4 Stocks

5 Bolt and Carrier

6 Optical Sights

7 Triggers

8 Leade

9 Handguards

10 Flash Hiders

11 Suppressors

12 Lower Internals

13 Piston Conversions

14 Competition Tuning

15 Magazines

16 Tools

17 Cleaning

18 9mm and .22LR

19 Assembly Tips

INTRODUCTION

This book’s primary aim is to dismantle the various urban myths that have attached themselves to the AR-15. Also, to make life a little bit easier for owners of the AR-15.

When it comes to using, repairing, building or debugging firearms, you need a basic level of knowledge or you won’t be able to get the job done. What I’m trying to do here is give you the one volume, the veritable firearms encyclopedia, devoted exclusively to building and repairing the AR.

You see, for a relatively simple industrial product, the AR-15 can be maddeningly difficult to assemble. This comes as a surprise to people who have assembled other, apparently more-complex items. For instance, bolting a header onto a re-built engine. There you face a rather detailed process, from cleaning and prepping the mating surfaces, to proper gasket selection and prep, plus getting the torque limits and bolt-tightening order correct.

This is all laid out in a manual the size of a phone book.

For the AR-15, there really isn’t such a manual. Sure, there are factory manuals, tomes that never leave the manufacturer. And there are military manuals, which are either so simplistic or kept under lock and key at the head armorer’s office on base.

If someone tells you they know how to build an AR and their MOS, or military occupational specialty was not that of an armorer who worked in an air-conditioned building, they probably don’t. I’ve been to armorers classes that cover everything from bore cleaning and sight adjustment to machining a receiver from a billet of aluminum.

But unless you’ve attended those classes, there’s been no one to tell you the details of these processes.

There are tips that make life easier. There are things you need to know that will keep you from hurting yourself. And because the mil-spec is so outdated in many regards today, there’s a plethora of parts to install. One subject that leaps to mind is handguards. A military armorer will know of one, two, maybe three handguards, and they will install them using one of two installation methods. However, if you have a different handguard, the knowledge base of a military armorer will be of no use.

A police department may be even less help. A departmental armorer may only know the one particular brand and model of AR that department issues or authorizes.

So, in this book I’m covering all the important details of as many different accessories as I can, of all the aspects of the AR that can be covered.

And because you really need to know the why, as well as the how, I’m giving you background about the products where it matters.

For instance, if you install a chrome-lined barrel with anything other than a ¹⁄₇-twist rate, you will be mocked in many online boards and in some gun clubs. You need to know why these scoffers are wrong, and why you may not want to limit yourself to such a pedestrian barrel choice. There are different grades of barrel, but for most shooters, in most instances, the differences don’t really matter.

A further example: an NRA High Power High Master. That’s someone who can tell you exactly how many clicks to adjust your rear sight to account for the wind-drift of your ammo at 600 yards. And can then tell you to undo two of them because the wind just changed. Such a shooter will gladly spring for a cut-rifled, stress-relieved stainless barrel that costs so much you’d think it came in gold leaf wrapping. That top-tier barrel can boost a honed shooter’s score five or 10 points. When your score is already in the upper 90 percentile of possible, any extra points you can buy are worth it. A barrel such as that, installed with loving care by an experienced gunsmith, can cost you $500. That’s knowledge that really matters.

If you are just having fun, and occasionally entering the local 3-Gun matches, a barrel that cost all of $150 will be more than accurate for your needs. That nets you $350 worth of practice ammo in your budget if you forego the gold-plated barrel. You tell me: will $350 worth of additional practice ammo make you a better shot? I think so.

A word of caution. Hang around any AR forum or talk to experienced shooters at gun clubs or local matches and you’ll encounter a broad spectrum of opinions. Some will cling very strongly to their views. And some will have what appear to be solid credentials. Take advice where you can get it and make up your own mind.

One last example, and I’ll let you get on to the fun part, the building part. If you were to talk to a Vietnam veteran about the M16, you will likely hear all kinds of “truths” — like how the gun is … fragile, unreliable, a plastic toy with bullets that tumble in flight. And so on. But are these assessments accurate? Well, yes and no. There were problems early on. Those problems got solved. There have been problems since, mostly due to loss of knowledge. We’ve addressed and corrected them.

But to the Vietnam veteran, knowledge of the M16 is frozen in time. Like a football fan who can’t let go of the past glories of bygone winning seasons, some find it difficult to move forward.

Oh, and if you come across a news story or a report from a Congressional committee about the M16, brace yourself for a tsunami of moronic info that threatens to take multiple IQ points off your score. Such stories should be treated as if they were implements of torture, meant to make you divulge the secret rocket plans.

New readers, the introduction should give you a sense of the snark you’re about to encounter. Old hands are familiar with this, and I hope they still find it entertaining and useful. Pour some coffee, get reading, and prepare to deploy wrenches and accessories.

CHAPTER 1
BACKGROUND

The AR-15 has been referred to as an “Erector Set for adults.” Designed as an industrial product, not a firearm (I’ll explain the difference in a bit) it has ended up as the most user-serviceable firearm ever made. Which is one of those “good news and bad news” sort of things.

By “industrial product” I mean that it was meant to be built using standard parts as much as possible. For example, the roll pins that hold parts, and the springs that work those small parts, are normal items you can buy in bulk from a non-firearms manufacturer. Indeed, if you want roll pins, you can consult catalogs devoted to them in every size, material, diameter and surface finish you could want. And when you order them, your choices are by the box or the dead weight. Compare that to trying to buy a model-specific part, like the trigger pin on an M1 Garand, M14/M1A or Remington 742.

That’s the good news — the industrial base to supply parts is so evenly distributed that there are no real bottlenecks. Well, none now, but for a while it was not so pretty.

The bad news is this: because so many can, many who should not, do. My start in this came in the middle of the 1980s. We had just gone through one of the first big semi-auto ban scares, during which a lot of people became proud new owners of an AR. Unlike the new AR-15s of today, those 1980s rifles had almost all been home-built. Back then, surplus really was … surplus. The parts you bought at a gun show, or by mail-order (no Internet back then) were actual military intended production. The parts had been declared surplus or excess. They were sold as scrap, by weight, or shoveled into dumpsters and then fished out once the truck had left the military base (some of them looked it, too). Some were production over-runs, but those cost more.

Rifles cobbled together on ‘Gun Show Special’ lower receivers, not surprisingly fail to work reliably. Once I had figured out what the usual suspects were as far as overlooked details and poor assembly, I fixed non-functional ARs for a flat fee. For $100, in the mid to late 1980s, I would make it run. If there were parts that the owner had bent, broken, machined, ground or otherwise altered they were an extra charge to replace and fit.

When I look back on it, this was an unparalleled opportunity to learn a subject. Had I learned how to gun-plumb ARs solely by going through an armorer’s course, I would have learned all the book smart school solutions which, loosely translated as “replace the non-spec part,” would have fallen flat.

I had to make the available parts work and somehow figure out how the cheap bastards who had made the parts had skimped and cut corners — and then make it right. And if it couldn’t be made right, one had to know how to get the right one in its place, and play well with the other parts. One had to be a gunsmith, not a factory armorer.

AR receivers start as either billets of aluminum or forgings.

So, that will be the focus of this book. How to install parts, assemble this or that and make it all sync together. I’m operating under the assumption that you’re not doing this because some department or company has wheeled a bin full of parts up to your bench. Instead, you have one, or perhaps a few rifles and you want to make them function properly — and you don’t want to buy five of something to find the one part that works.

I’ve received complaints in the past for not having written a ‘build an AR’ type of a book, one that takes you step-by-step from a box of loose parts to a finished rifle. While we used to build rifles that way, I don’t see the point these days. Since the 21st century began, the number of AR-15s and clones in the USA have more than doubled. That’s right, the number of AR-15 type rifles made and sold in the US since Y2K became a historical chuckle is greater than the entire production period prior. From its unveiling in the early 1960s, to 1999, there was really one company that made them in a big way and that was Colt. Colt wasn’t all that interested in selling them on the commercial market, which is why the smaller boutique AR makers got their start.

One early bird was Olympic Arms who, to be fair, do not have the greatest reputation as an AR maker. The bad reputation is mostly false, as Olympic wasn’t interested in hewing to the mil-spec line for much of its production. If you live and die at the altar of mil-spec, then nothing Olympic made was any good. Those of us who were winning matches with their excellent stainless match barrels, though, would argue otherwise. I never had any problems assembling ARs from Olympic parts. And the amount of work to bring them up to speed was no greater than any other brand of rifle I ever worked on.

Soon after, Bushmaster came about. They too worked to satisfy customers, but the mil-spec mavens would have none of it.

The Danish guard in front of a government building in Copenhagen. The interesting thing about the A2 rifle here is its clamp-on carry handle with an A1 sight. Oh, and that isn’t a real magazine in the rifle, he’s going to need that bayonet if trouble comes.

During all of this, there were lowers made by people you never heard of. PWA, Eagle Arms, (before Armalite bought the rights to the name) E. A. Co., Palmetto Armory, Pac West, SGW, Cavalry Arms — these were all either AR EOM manufacturers who were looking to keep the machines running despite the lack of orders from the big name makers, or the result of marking variances from the big names.

Look at it this way, and I’m just grabbing numbers out of the air. You are an over-run manufacturer for lowers, a supplier to Colt or others. Colt asks for 10,000 lowers a year, to satisfy the orders for commercial rifles, since Colt is (and was) focused on military contracts almost exclusively. Meanwhile, your production capacity is several times that. So, you make a batch with a made-up armory label and offer that to wholesalers. The tooling is set up, the machinists know the job and getting extra forgings is no big deal. The forge operation even quoted you a volume discount for the extras. The extras cost you practically nothing

When you offer them to the wholesalers, product disappears as if they had simply evaporated off your shipping dock. Whoa. Would you make more? If you were a proper business man you would.

So, you fill the next order for 10,000 lowers to fulfill the Colt contract, and while the tooling is still set up you again run off 10, 20, 30,000 more, but with the no-name armory markings. That part is easy. All you have to do is file a marking variance with the ATF, and the lowers can have any name you want on them. If you want to make sure there are no hard feelings with Colt, or anyone else, you open an office in a nearby town and mark the armory as being in that town, not your FFL-designated locale.

This is a normal business operation, even when there is extra demand, but certainly when the contract does not prohibit it. A lot of what you see as “surplus” ammo is made this way. The ammo company has an order for five bazillion rounds, and they can easily make more. So they do, and sell the rest, in differently labeled boxes as “surplus” or “equivalent” or some other inducement.

Back during the Reagan and Bush eras, I’d see lots of rifles and carbines show up, and people would ask, “How long has No-Name Armory been making rifles?” Answer: they haven’t. They never were. The lower was made as a bare lower, and the guy at the gun show who sold it to you as a rifle had assembled it from bins of surplus parts. Should he have had a license as a manufacturer to do that? Yep, but back in 1987 no one was worried about problems arising from not being a manufacturer. Now, not so casual bub; get a license or stop building.

But the die was cast. If Colt was going to neglect the market, and people could make money attending to those otherwise neglected customers, then why not get a manufacturers' license, assemble ARs and make money? With marking variances, you could order lowers with your name from any of the people who actually cut metal to make lowers, uppers, order-in barrels and all the other parts, too.

Some will claim that isn’t really manufacturing. Well, OK, you may be right. But it was exactly the idea behind designing the AR-15 as an industrial product. By spreading the base, making it less of a specialized process, the country would not be at the mercy of one plant being sidelined in an emergency. Remember, in the early 1950s, memories were still sharp concerning shortages faced in World War II. And we’d just more-or-less concluded the Korean fracas. Having a distributed small arms production base was considered a good thing. Having it concentrated in one company, in one plant with very few suppliers was a bad thing and easily disrupted.

The British SA80 (and later “improved” versions) is such a fabulous piece of awfulness that it requires protective covers over the handguards and optical sight.

THE AR-15 PIPELINE

At the nadir of production, we had some pretty severe bottlenecks. The AR-15 depends on forged upper and lower receivers. While there are still a lot of forging operations that can still handle it, you need special dies to forge uppers and lowers. And the machines that forge aluminum, coupled with the furnaces that heat it, are not the same ones that heat and forge steel. As volume decreased, forge shops that found ARs a marginal business dropped them from their work. Even today, there are only a few forge shops that handle the AR market.

Another bottleneck was barrels. It takes specialized machinery to drill, hone and rifle a barrel. A generation ago, barrel makers were still using WWII-era rifling machines, because that’s what they had. At the height of one of the previous so-called assault weapons bans, barrels were particularly hard to come by. It was not uncommon to find that the only barrels available were the “177” ones. They were 11.5-inch rifled tubes, with a 5.5-inch flash hider welded in place. Why? Barrel blanks then came as roughly three-foot long steel bars. You can make one 20-, two 16-, or three 11.5-inch barrels from one blank. If customers are screaming for barrels, and you can get full price for any rifled tube that leaves the shop, you’d be crazy to make anything but 11.5 + 5.5-inch, or “177” barrels.

And then we come to the last bottleneck, magazines. At the low point, there were three, maybe four magazine makers turning out USGI mags. You didn’t want any other back then simply because anything that wasn’t USGI was truly wondrous crap.

Just prior to ⁹⁄₁₁, if there had been perhaps a dozen mysterious fires across the US, the entire AR-15/M16/M4 production system would have been utterly stalled. On top of that, there was only one ammunition plant producing 5.56 for the government. We can only be thankful that while our enemies are truly venal they do not have a grasp of a modern, industrial society and system.

But today there are magazines galore. You can buy any of a dozen different brands, made by the actual company whose name is on the product. You can buy USGI from a number of different makers and you can buy them in bulk very cheaply. How cheap? As of this writing, Brownells (and who thought Brownells would be making magazines?) is offering a ten-pack of brand-new, guaranteed, 30-round magazines for $115 and shipping. That’s eleven dollars and change per magazine. Calculated back to the halcyon days of 1987 that would have been $5.50. Let me tell you, any magazine you might have been offered for five bucks back when Reagan was still in office you viewed with great suspicion. Today, you have your choice of a vast array of top-rate magazines, for half the cost of the ones we used back then.

Barrels? You want a hand-lapped, single-point cut-rifle barrel? You want button? Broached? Hammer-forged? Chrome-lined or not? What weight, length, profile, fluted or not do you want? Brownells, again, as of this particular moment, offers no less than 73 different barrels from which to choose. From a stripped barrel, no sight, for $85, to a ready-to-go Colt for $350, to a carbon-fiber wrapped tube from Proof Research for $940 smackers. (And a wondrous barrel the Proof Research is, having just spent some time with one. Envy the guy or gal who has one.)

Given the volume of rifles made and sold I have to assume that the forge operations have worked out the details of producing a metric buttload of forgings per quarter, because that’s the volume we’ve been buying them at.

But still, why? Why this book?

I began a regular schedule of working as a law enforcement firearms instructor almost twenty-five years ago. At the time, “patrol rifle” included a lot of firearms, mainly the MP5. But there were a lot of AR-15s to be seen. Back then, an AR that showed up in the classes was as likely to be a Frankengun as a factory-built Colt. I was back in gunsmithing and fixing mode again. Since then, the classes have shifted almost exclusively to AR-15/M16/M4 projects, to the point that if anything else shows up, it is notable. We still see Frankenguns and they still need work. We’ve also added a raft of tricks to the arsenal, since not all factory guns that show up are fully functional. This book is to detail the tricks, tips and enhancements I’ve learned in those years.

Plus, a lot of shooters have entered the AR market at the basic end of the pool. It is one thing to buy a $600 AR, learn to use it, learn if you like it and then move on. That can mean either selling it because it isn’t what you expected, or building it up into the rifle you really want now that you know what you want. Now that you know you don’t want the boring black M4 handguards that came on your rifle, what can you do? Which free-float handguard should you select? How do you take the old parts off and install the new ones? If it were obvious, the handguard manufacturer would not have included printed instructions.

And that is what this book is for. My goal isn't to give you the step-by-step instructions on how to assemble a rifle from a box o’ parts. But, if you pay attention to the various chapters you will essentially learn how to do just that. This book doesn’t show how to build a gun because it is more than that: It is how to re-build a gun — and then some.

One of the great things about the AR is that the anodized aluminum surface can be painted. Camo, neon, whatever. This Alexander Arms 6.5 Grendel is powder blue.

MIL-SPEC CONFESSION TIME

OK, I make fun of the mil-spec people a lot. Well, I make fun of a lot of people, a lot. It’s just so easy at times, and I really should demonstrate a higher level of self-restraint. What you have to keep in mind is that the military specifications for anything are a minimum level of goodness. The government wants to make sure they get what they’ve paid for, so they specify what something has to be. Since the contract goes to the lowest bidder, there is no incentive to exceed the specifications. Making the parts better simply cuts into the profit margin. There’s an adage about that, where the government is concerned, The minimum becomes the maximum. Say there’s a test, and you have to do push-ups. Twelve is the max you need to ace the test. Why do more? You won’t get credit for it, and it will simply tire you for the next stage of the testing process. It is entirely possible to make something better than mil-spec. But if you use a better grade of steel, you don’t get credit for it. And if you don’t use the steel specified, even if it is better, you lose the contract.

So keep that firmly in mind. Mil-spec is the minimum.

I have joked that the Army was trying to replace the M16 even before they adopted it. Ever since, they have been trying to replace it with something that was a so-called marked improvement over the existing legacy product. Let’s just hang a number on that, shall we? Let’s say, in 1972, the Army was trying to replace the M16A1 with a small arms system that was 50 percent better.

One could argue, and not without cause, that if the Army had simply adopted all the incremental improvements since then, they’d have far exceeded a 50 percent improvement.

Industry improvements in alloys, platings, heat-treatment, surface treatments, computer modeling for stress management and so-on have made every other product in use since 1972 much superior.

One example. Do gunsmiths these days quote the cost of re-blueing the slide on a Glock? No? Why not? Because the tenifer process makes caustic bluing methods entirely redundant when it comes to Glocks.

Keep that example in mind the next time someone tells you that mil-spec is not just good, but superior or even unsurpassed in quality.

PERSPECTIVE

I have organized this book around the subject of the chapter, around one particular aspect. In barrels, for example, I provide background and how to install them. Ditto sights, handguards, etc. There will be those who will complain that I have not laid it out as an assembly manual. What they want is to have an open box of all the parts, the tools and a book that tells them how to turn the box o’ parts into a working rifle.

I would like to think that you are clever enough to figure out that if you have a book of chapter-by-chapter instructions to use as a guide on how to deal with common parts that you can string them together for a functional and improved AR-15.

Even so, I have added a bonus chapter to the book. There, in Chapter 19, you will find the order of assembling a rifle from a complete set of loose parts. You’ll find the order, with addenda and sidebars, but the detailed process for each will still be in their respective chapters.

As an aside, I was to do just such a project, with Brownells sending all the parts, and the process being written up in one of the gun magazines. There was a change in the editorial plans, and the Brownells parts ended up in this book, as well as in other magazine articles. I mention this only because when the box arrived I was surprised at how small it was. I was expecting, when I opened it, to find a packing list indicating there would be another box or two arriving. The complete set of parts to assemble an AR-15 carbine arrived in a box not much larger than a salesman’s sample case.

Some things you find out only by doing.

CHAPTER 2
BARREL INSTALLATION AND CHANGE

Now we’re to the point where your barrel is toast. How long does that take to happen? Good question. The mil-spec guys will tell you that the spec is 7,500 rounds. Well, OK. If you are willing to swap out your chrome-lined, Colt barrel at 7,500 logged non-military-use rounds, and install another, I’d be happy to buy that supposed shot-out barrel from you. I'll give you $20 for the thing, with the swap.

My Faux A2 began life with a no-name barrel. After a couple of fun-filled winters shooting in Mad Minute matches, and lots of practice competing in monthly 3-Gun, it was starting to show a bit of wear. By then it had chugged through roughly 15,000 rounds and wasn’t holding minute-of-angle (MOA) groups. It was still well under the mil-spec acceptance accuracy level, which equates to about 3 MOA (roughly 3 inches at 100 yards).

The clamshell fixtures hold upper receivers just fine. The M4 one holds both old and new. The A1/A2 holds only A1 or A2. So, get the M4.

The second barrel lasted a bit longer than that, but it too started to lose accuracy. The rifle is now on its third barrel (with the same bolt) and it is doing fine.

If you see this from your rifle, one of two things is going on. Either your barrel is worn out or you have a bullet that is too long for the twist rate of your bore.

To illustrate, at a recent class, one of the students was having trouble getting his rifle zeroed. The groups just wouldn’t settle down. He had no idea how many rounds he had put through it in the twenty years or so he’d owned it, so we stuffed an erosion gauge down the throat. Typically, the erosion gauge will show some wear past the “new” point, and once it shows an inch or two of wear you can count on the barrel being used up. The erosion gauge went more than halfway down his barrel — about two-thirds of the way to the muzzle! For a moment, I thought it was going to fall out of the muzzle end. And he’d only recently noticed a drop in accuracy.

Now, had an NRA High Power Master shot it, he or she would have noticed an accuracy problem years ago. But, he was concerned about its potential use in his law enforcement job where a gunfight might be conducted at the length of a Buick.

So, how worn-out is too worn-out? That depends. The military 7,500 round figure takes into account a healthy routine of full-auto or burst-fire use, in harsh and unforgiving climates and with little or no maintenance. If that’s you, then yes, 7,500 rounds is a reasonable figure. At today’s ammo prices that represents a minimum of $2,000 to $2,500 in ammunition, so the price of a new barrel really isn’t a big deal. You should be able to put a good quality replacement in there for a tenth of the ammo cash you burned up practicing and competing.

Another possibility is that you haven’t worn out a barrel; instead, you’re perusing the pages of an AR maker’s catalog trying to decide which barrel to get.

So, let’s first look at barrels, length, weight, gas system and rifling methods and expectations.

BARREL LENGTH

There are three common barrel lengths. Two are specific and one is general. The two specific are rifle and carbine, 20 and 16 inches, respectively. The general one is “SBR” or short-barreled rifle. There’s also a single length found in 3-Gun and multi-gun competition, which is 18 inches.

Rifle barrels are 20-inches long for one simple reason: that was what the original was made at, and what the government first bought. It delivers a very good velocity for its length and, unless you are a really short person, it is a handy size except in tight quarters or vehicles.

The carbine is 16 inches for a very simple reason — that is the shortest allowed under Federal law. It is a handy length, but it isn’t the handiest in the situations that require the handiest, so the category of SBR fills that need. Anything shorter than 16 inches is what is called a “short-barreled rifle” in regulatory parlance and is controlled by the National Firearms Act of 1934. NFA/34 means you have to ask permission to buy one (if allowed in your state) and pay a one-time tax of $200. SBRs can be as short as 7 inches, but those also can be very persnickety to run reliably, they have shorter service lives and you lose lots of velocity. You gain noise as well.

If you use aluminum barrel blocks, and you find the barrel nut is too tight, you’ll end up with aluminum scuff marks on your barrel.

What length, weight, twist and material barrel you decide to install is between you, your aspirations and your wallet. Just one suggestion, though. It is a whole lot easier to buy too heavy, than it is to buy too light. Heavy barrels are hard to carry, light barrels are hard to shoot. At least a light barrel can be carried — and thus shot.

And in case you ever wondered, why a 14.5-inch barrel? Colt had spent a lot of time and money making the various “Commando” models work properly (this was before the M4). They had 11.5-inch barrels on the guns, which sold well for Colt. Then, an overseas customer wanted compact rifles, but had an odd request. Could Colt make them take a bayonet?

This is one of the old barrels, from an earlier assault weapons ban panic. It is an 11.5-inch barrel, with a 5-inch flash hider.

Colt no doubt scratched their heads over this, but if the customer was willing to pay, then why not? So, the carbine-length gas system, with a barrel extended just long enough to mount a bayonet, was developed. It came out to 14.5 inches in length, which also happens to provide pretty much the same gas dwell time as the regular rifle.

When Colt settled in to develop what later became the M4, they used the 14.5-inch barrel as the standard, because, well, if you’re going to have a more-or-less general issue rifle or carbine, it had to have the means to mount a bayonet. And in the convoluted logic of the military, it was easier to have a carbine with a non-standard barrel length, and use any of the warehouses full of normal bayonets, than it was to make a rational barrel length and special bayonets for them.

If you want to use a USGI M4, 14.5-inch length barrel, on a non-SBR build, you have to find some way to extend the barrel past 16 inches. This you do with an extra-long flash hider, which is pinned and welded to permanently secure it on the barrel.

Most of us take a different path. We either just build it as a 16-inch-plus barreled carbine, or we SBR it and go with an 11.5-inch tube. Me, I don’t see the attraction of a 14.5-inch pinned and welded barrel.

TOOLS

If you’re going to swap barrels, you need tools. No matter how strong you are, you can’t hand-wring a barrel nut off, nor get it back on. Let’s start with the originals, the USGI barrel wrench and barrel blocks. In the pantheon of awful gear, the USGI barrel wrench, and the aluminum two-sizes-that-fit-nothing blocks, are awesomely craptastic. If someone tells you they are the proper mil-spec tools for the job, you have my permission to ignore them and go buy good gear. If you take their word for it, and try to use those tools, you’ll wish you had listened to me.

Here’s the problem. The wrench has three stubs that are supposed to fit the notches of the barrel nut. The two opposing stubs are 180 degrees apart. Was it too much to ask for someone to have paid attention to simple geometry, spacing them just a bit further around the circumference? Despite your best efforts, the spring-loaded slip ring will push the wrench so the stubs no longer have a secure hold on the barrel nut. When that happens, your torque will be applied to your knuckles banging into the bench, or will lever the wrench handle bar into your groin.

Too much torque? Yes, there is such a thing.

And no, you can’t use the lever you use on the wrench to help, either. You are supposed to use a regular torque wrench, or a ratchet handle from a wrench set, as your lever. But since the wrench handle locks into the barrel nut plate by means of the square hole in the plate, there’s no real attachment, no security. The handle can’t resist the tipping force of the delta assembly, and you find yourself needing three hands — one to keep the plate pressed in against the delta assembly, one to keep the wrench secure on the USGI plate, and one to loosen or tighten the nut. The more you position yourself to keep the plate in place, the less leverage you have on the wrench handle.

Plus, the three lugs don’t offer enough gripping area. If you encounter a really obstinate barrel nut and have only three points of contact, you’ll end up bending one of the nut or wrench lugs. It is usually the nut that gives way, and once it does, you have to switch to another set.

The USGI wrench exists only because the Army has not seen any need to change it. Yes, people have been doing it like that for decades, but that’s no excuse to stop you from looking for a better way. The barrel blocks fit only the USGI-diameter barrels for which they were made, and those are held only sparingly. If you encounter a particularly resistant barrel nut, or one that needs just a bit more elbow grease to time-up, the barrel will slip in the blocks. “Just use some rosin,” say the mil-spec folks. No, I say — get a better holder.

The first step is to get a proper wrench, one with multiple teeth to grab the barrel nut; such a tool will be less likely to be pushed off by the slip ring. In addition, by spreading the force across more teeth, you are less likely to slip or deform the USGI wrench. I have wrenches from a few makers and when they were new it mattered which one you ordered. Now, Brownells has a whole page of nothing but good barrel nut wrenches, so get one.

Second, you should have, at the very least, the Brownells clamshell holder, which grasps the upper receiver (instead of the barrel). This clamps onto the receiver with no chance of slippage. However, if the Brownells clamshell has a fault, it is this — it works only with forged uppers of the A1/A2 or flat-top type. If you have anything else that is milled, extruded, reinforced or non-standard, the clamshell won’t fit.

As good as these are, there are even better tools. The top tool for holding all this is the Geissele Reaction Rod. It’s basically a steel bar you clamp in the vise (with flats, not round) and a toothed section that engages the locking lugs of the barrel extension. The torque you are creating is held by the locking lugs, not the receiver or the clamping force of the aluminum blocks on the barrel exterior.

As for a wrench, you cannot do any better than the one offered by 2 Unique. It starts as the USGI wrench, but instead of that tool’s three barrel nut lugs, 2 Unique secures a trio of lugs at each location. That gives you nine times the gripping surface, and there is no way you can bend any one lug.

Better yet, 2 Unique doesn’t expect you to attach a ratchet handle to the wrench. Oh, they make a compact one that looks like a USGI wrench, for those impressed by the mil-spec look, but the full-sized version is the one to get. That wrench features a welded steel handle, giving you 2 feet of leverage with which to loosen or tighten a barrel nut.

Now, this wrench is perhaps too much of a good thing. You have lots and lots of leverage coupled with a super-tough engagement surface. You can slip a tube over the wrench handle for even more leverage. It is entirely possible to generate enough force with this, and with the barrel held by a Reaction Rod, to break the aluminum threads on the receiver if over-tightened. The idea of better tools is to make the job easier, not to break things faster. So, if you are going to use manly tools to tighten things, be careful. For removing an overly tight barrel nut, this would be the ticket to stardom.

The threads on the upper receiver are aluminum. The barrel nut is steel. Keep that in mind.

The barrel is screwed into the barrel extension, which contains the actual locking lugs for the bolt to hang on to.

REMOVING THE OLD

I’ll assume for the exercise that you have already unloaded the rifle, taken the upper and lower apart, removed the bolt assembly and charging handle, removed the handguards, taken the gas tube off and have decided if you are going to salvage the slip ring assembly or not.

If you are using the clamshell holder, slide the center rod of the clamshell assembly into the receiver and close the ejection port door. Fit the upper into the clamshell, close it, and then nestle the assembly down into the vise jaws. Tighten the vise. Don’t crush it, but make sure it is tight enough so the clamshell can’t move. Make certain that you position the clamshell so it is held completely within the vise jaws. If things have to stick out, make them stick out the back end, where you won’t be wrenching. Better yet, use a bench vise big enough to completely encompass the clamshell.

If you are using the Reaction Rod, clamp the rod in the vise and tighten as much as is humanly possible. You aren’t going to damage rod or vise, so make it tight. Then slide the barreled receiver over the rod, making sure the teeth on the rod engage the locking lugs of the barrel.

Now position the wrench on the barrel nut so the wrench handle is sticking up at about the 10 o’clock angle. You want to have some downward movement to your exertions, but you don’t want to be working below your waistline. To do so will tempt you into putting weight on the wrench handle, and if it slips, you crash to the floor. No, I learned this not from personal experience, but from someone who landed on the wrench when it came loose — inadvertently locating the wrench in a delicate location.

And remember the time-honored mnemonic: lefty-loosy, righty-tighty. As you stand there, on the muzzle end of your clamped upper receiver, the barrel nut will come off when turned counter-clockwise.

If you have done things properly, and the assembler didn’t over-tighten, you will find that a pull on the wrench unlocks the nut. It will resist and, sometimes with a snap, pop free.

The barrel is drilled for the gas port, and port dimensions vary depending on the end-use of the barrel and its length.

What to do if it doesn’t pop free with a pull? Re-position the wrench. Position it as horizontal as possible. If the wrench can’t be dead-level, then set it a notch above level. Stand belly-up to the wrench, putting one hand on the handle and your other so it pushes the tool into the barrel nut. Yes, I made you buy a wrench that doesn’t need this, but now it does. Press the wrench into the nut with your right hand, press down with your left, and lean in, putting some body weight into it.

If this does not loosen the nut, then you have to take a step back in the process. Loosen the vise, take the upper out, remove the clamshell, and stand the receiver with the muzzle down, in a corner. Put the muzzle in an old coffee can. Squirt or spray penetrating oil into the joint between the receiver and the barrel nut. Gravity and wicking action will carry the oil down into the threads. You are not going to try again that day, so move on to something else. The longer you wait, applying oil a couple of times a day, the easier your task will be. Patience beats exertion.

Once you can’t wait any longer, go back through the steps above. You should find that the barrel nut comes loose with exertion. If it doesn’t, then you have a difficult choice — machine tools or quitting.

Once the barrel nut comes loose, put the wrench away and hand-turn the barrel nut off. Grab the barrel and pull it straight out of the receiver. If it doesn’t come out, resist the temptation to wiggle it. Think about it. You’ve got a long steel lever that fits tightly into an aluminum shell. If you rock that 16- or 20-inch lever enough you could bend the receiver.

TO LOCTITE OR NOT TO LOCTITE?

If the barrel nut has been secured with Loctite, you have full permission to take the previous owner’s name, or builder’s name, in vain. In fact, a lot of us will help you. Even when building rifles to have the barrel really secure, you apply Loctite to the barrel extension, not the threads. If someone has used Loctite on the threads, things will be very messy, and you may not be able to salvage the upper.

To remove an unloosenable barrel nut, you need a milling machine. I’ve done it with a cut-off wheel in a dremel tool, but I do not recommend it.

You also have to accept that you will not be salvaging the rest of the delta ring parts.

To mill off the nut, lock the stripped receiver horizontally in the mill vise, ejection port side down, clamping the barrel in your vise. Use a carbide cutter with a high RPM and a low feed rate. In fact, your feed rate will be all hand-done, no automatic feed. Slash through the front flange of the barrel nut, delta ring, spring and e-clip. Once you have passed through all that stuff, rotate the delta ring, spring and clip, and cut them again, so the two halves fall off. The receiver and barrel nut are now in full view. Now, drop the cutting tool half the thickness of the barrel nut tube, and run the cutting tool down the length of the barrel nut. You probably will see the notches of the threads in the cut. If not, drop the cutter .010 inches at a time and cut in the same trough until you start to see bright metal on the receiver thread tops. Yes, you are cutting the receiver threads, but you are only putting a flat spot on them, at one spot on the receiver. Once you can see bright spots on the tops of the receiver threads stop cutting.

The excessive torque on the barrel nut acts to create what is known as hoop stress in the nut’s tube. After you have cut enough of the steel away, the tension will be greater than the remaining steel can stand, and the nut will break with an audible snap. At this point you can practically spin the nut off by hand. You are done cutting.

If the nut does not spontaneously snap on its own, remove it from the mill vise, re-install it in the clamshell, and use the barrel nut wrench again. Here’s a tip. When you place the wrench on the barrel nut, engage the teeth of the nut such that the wrench is pulling away from the cut you just created. Do not place the wrench so you are pulling towards the cut. By pulling away from the cut, you increase the stress on the cut area of the barrel nut, and it will probably snap at that time.

Because of the flat-topped threads, the receiver will be somewhat less able to deal with the torque of the new barrel nut, so don’t be ham-handed when you install the new barrel and nut.

The barrel is held in the receiver by the barrel nut (missing in this photo) with the gas tube riding above. There’s a lot going on right in that small area.

A longer bullet needs a faster twist to stabilize. The 55-grain bullet (left end) is happy with a ¹⁄₁₂-inch twist rate. The 100 grain (right) will sulk with anything slower than ¹⁄6.5-inch twist.

If the barrel won’t come out, it may be carbon-welded or Loctited. Remove the receiver from the clamshell, fire up a propane torch and apply heat to the receiver threads and barrel. If you’ve ever burnt out Loctite you know that once it gets to the decay temperature it starts to smoke. If you get to that temp (it won’t take long) and you don’t see, smell and hear the sizzle of burning Loctite, you know it was carbon-welded. The heat will help loosen it, but you need to apply more penetrating oil. Put it back into the bucket/coffee can, and oil regularly.

If you want to speed the process, you can knock the barrel out. For this you’ll need a steel bar that is slightly smaller than the diameter of the chamber and longer than the receiver. Drop the rod into the chamber, hold the receiver in one hand, and tap the rod with a ball-peen hammer. You want to gently loosen or tap out the barrel, do not try to do the work in one hit. With a few taps you can push the barrel forward, and then once the locating pin clears the receiver slot, twist it to loosen the bond, allowing it to be pulled out.

And while all this work and effort is going on, consider your situation. You’re expending how much time and effort to pry the parts off of an upper receiver, a part that costs less than a hundred bucks? OK, just so long as we’re all clear about this.

NEW BARREL INSTALL

First you need a receiver, either brand new or the one you just spent an afternoon or three wrestling with, as above. And of course a replacement barrel. Let’s put them together, so you can get to the range. First, clean everything. Scrub the receiver, paying particular attention to the external threads and the interior bore where the barrel will rest. Clean the barrel extension, the chamber end with the collar on it.

Now check the fit. If the barrel slides in easily and even rattles around a bit, this will not be a happy marriage. You want as snug a fit as you can get, short of having to use a hammer to get them together. If you have the parts, swap uppers and barrels until you find a satisfactory fit. If you have only the one receiver and one barrel, then you’ll have to live with it, at least for now.

The barrel nut clamps the barrel into the receiver.

Once you’ve achieved proper fit, you need to prep the barrel. Barrels typically come with the front sight and delta ring assembly installed. If you are going to build the rifle with regular handguards, you’re set. If not, then you’ll have to remove the delta ring assembly. It comes off the front, which means removing the front sight tower. For this you’ll need the Brownells front sight block. Even if your rifle does not have taper pins (shame on you) the block still works. If the front sight is held on with set screws, or clamping screws, undo them. You can re-install the front sight once the barrel is in place.

Check again to make sure the mating surfaces are clean.

Slide the receiver onto the barrel extension, line up the receiver slot with the small pin and press it into place by hand. Now install it in the clamshell or slide it over the reaction rod. You do not want to be using tools, or force, at this point. The risk of damaging the receiver is too great.

This barrel is marked “5.56 NATO chromed.” That means it was chromed, but it wasn‘t a 5.56 NATO throat. Markings can’t be trusted, with a few exceptions.

Once the receiver is snugly in place, apply light oil to the threads and wipe around until they’re covered. Use a shop cloth to clean up the excess. Some people will tell you not to use oil, claiming it will cause the nut to come loose. Not likely, considering the torque values we’ll be applying. Others go the other extreme, shrinking back in horror at the thought of galling, seizing or mangling threads — leading them to apply so much anti-seize compound it oozes out the sides when tightened. Both are wrong.

You want a little light oil to prevent stiction of the threads, that being where the friction of dry surfaces sliding over each other prevents a proper reading of torque values. Yet you are not going to be applying so much torque that you need to worry about seizing.

Slide the barrel nut over the barrel, and spin it onto the receiver by hand. Once it stops, take a look. Notice how the notches, or teeth of the barrel nut, create gaps for the gas tube to pass through? That’s the plan. My method of installing a barrel nut is a bit involved, but I’ve found that doing it properly, once, saves a lot of extra work and heartache later. With the barrel nut hand tight, place your barrel nut wrench on the toothed rim of the barrel nut and tighten. Once it stops, note where it stops. Use a marker or Sharpie to denote the topmost tooth. Loosen it, remove the wrench, and hand tighten the nut again. Did it advance past the first spot? Good. Loosen once again, and repeat the process. This is where your barrel nut stops.

At this point, the mil-spec crowd will interject, deriding you for what the torque specs are supposed to be. Uh, huh. Before we go into that, look at the gap in your barrel nut through which the gas tube passes. Is the notch dead center? You can eyeball it or you can gauge it. The best gauge is one made specifically for the job. Stick the gauge into the gas key on your carrier, and slide the carrier (you can take the bolt out, or leave it in, it won’t matter) and look for the gauge when it pokes out of the upper receiver. If you do not have a gauge, a #16 drill bit will do. Since the drill, 0.177 inches in diameter, costs you $3.99, and the gauge, diameter 0.178 inches, costs you $5.99, unless you already have the drill on hand I don’t see the point in saving $2, just to get the product that is a pretty good substitute.

The barrel nut has to be correctly timed, or the gas tube can’t pass through.

This is a mis-match of feed ramps that will cause you headaches. An A1 barrel, with an M4 receiver? That will bring things to a screeching halt.

Be sure your alignment is correct: the gauge will poke out of the receiver and pass through the flange of the barrel nut without touching said flange. If it gently rubs against the flange, you can tweak the barrel nut a bit tighter (if it hits on the left side of the nut gap) but I would not be keen on loosening the nut if the gauge passes through and rubs but does not bind against the barrel nut flange.

So your barrel nut install passes the gauge test? Congratulations, your job is done. Torque? Who cares? If you used a proper wrench, and you are not a literal 85-pound weakling, you have easily exceeded the minimum military spec for barrel nut torque. The military spec calls for no less than 30 ft. lbs. of torque, with up to 80 ft. lbs. allowed, in order to correctly align the gas tube.

Back when I was working real jobs for a living, I could practically wring a barrel nut on with my bare hands, torquing it by feel to 30 ft. lbs. With a wrench in the barrel nut, I’m not sure it is physically possible to stop below 30 ft. lbs. Do the “tighten three times” drill. If your barrel nut lines up perfectly, you are done.

A regular barrel nut wrench only holds the barrel nut with three studs. It is prone to slippage.

If not, you have decisions to make. Take a long, hard look at the alignment of the barrel nut teeth. There’s a flange in the path of the gas tube. Is that flange straight up? Or does it tilt to the right or left? If it is more than halfway past the gas tube gauge location, you can tighten the nut some more, and get things lined up. If it isn’t, you cannot simply tighten the nut some more to make it line up. There is a limit — the aluminum of which the upper receiver is made.

As we’ve discussed in previous volumes, threaded fasteners work like springs. Thread tension increases as you tighten, and that tension keeps the assembly tight. The tensile strength of ordinary steel can be as low as 47,000 psi, and depending on the alloy and heat treatment it has received, can be as high as 220,000 psi. Aluminum? The 7075 alloy of which your upper is made has an ultimate tensile strength of 83,000 psi. You can torque the threads right off that receiver if you get ham-handed and have a breaker bar on your wrench.

So, there are limits to how much more you can heave that barrel nut over, to provide clearance for the gas tube. What to do? One option is to spin that barrel nut off and try the next one in the bin. Oh wait, you don’t have a bin full of parts to select from? Darn. OK, next step; washers.

The new wrench design, with a cast-in socket, grabs the barrel nut around two-thirds of its circumference.

INDEXING SHIMS

Randall Rausch of AR15barrels.com calls these barrel nut indexing shims, but everyone I’ve ever shown them to goes, “Oh, washers.” They are flat, shim material hoops that are 0.001-inches thick. The process is simple; you tighten your barrel nut according to the above instructions, and determine that either it can’t be tightened more, or it’s too loose when correctly aligned.

Rausch refers to the two situations as either “one-third too far” or “two-thirds too far.” The shims are designed to correct one-third of an index location. If you tighten the barrel nut, and the tooth on the nut that is uppermost is crowding the gas tube hole from the left, as viewed from the muzzle, it is one-third too far. If it is crowding the gas tube hole from the right, it is two-thirds too far.

Once you have ascertained the degree of misalignment, unscrew and remove the barrel nut. Slip the shim/washer, or two, over the barrel, and carefully press onto the barrel shoulder. You can use a drop of oil to create a seal between washer and barrel shoulder. Then slide the barrel nut back on and hand-spin it into place, tightening as explained above with the wrench. You should find the barrel nut tightening to perfect alignment.

If you have not removed the sight, because you’re installing a barrel as-is, use scissors to clip a slot in the washer. Don’t just clip it, clip a section out of it, ¹⁄₁₆th of an inch or so. If you don’t, the washer can stretch as the barrel nut rides over it in the last bit of tightening, and it could overlap.

When I first learned of these indexing shims, Rausch was the only one offering them. Since then, a multitude of makers have jumped into the field, many from China. People who love to save money love China. People who expect items to conform to a certain stated specification are not so enamored. You see, the washers from China are often metric. That means that they are not necessarily 0.001 inches thick. If you order a set of shims that are advertised as 0.0254mm, then they should be .001 inches thick. Still, measure them with your calipers. They could be a fraction of millimeters, such as 0.050 or 0.033 inches. In that case you’ll have to do some math to convert the adjustment, or simply slap one on and see what it does.

2 Unique makes their barrel nut wrench with nine studs, grabbing the barrel nut flange in trios of studs. No slippage, and a two-foot long handle for leverage.

WHY ALL THE FUSS?

The gas tube can be bent to squirm past the offending barrel nut tooth and still work. But you’ll have problems if you take that more than just a little off of alignment. That’s because of tabs inside the slot of the regular USGI handguards that ride on the barrel nut. Also, the front handguard cap has both a clearance hole for the gas tube and stamped detents to hold the handguards, which aren’t supposed to rotate freely around the barrel.

If your feed ramps have a mis-match, you may see bullets with marks like this. This one failed to feed, but didn’t get driven back into the case.

If you leave the barrel nut cock-eyed, the handguard will only fit under the delta ring if it, too, is off. When you do that, it won’t align in — or with — the front tabs. And you can’t tilt the front cap to match the handguards because the gas tube and its hole in the cap don’t have much wiggle room.

And all this gets worse if you’re installing a free-float handguard, one that clamps directly onto the barrel nut. In that case, not only will your handguard be tilted, but the top rail will be, too. If your front sight is on the handguard, it will be tilted off-center and you won’t be able to zero your rifle. Nor will you be able to use your iron sights, but your friends will be able to mock you mercilessly.

Get the barrel nut properly aligned. Life will be a lot easier.

TORQUE LIMITS

How tight is tight enough? The military manuals are not much help. They offer such a wide range as to be useless. Many claim 30 to 80 ft. lbs., until the barrel nut is aligned to allow proper installation of the gas tube. Gee, thanks.

If you need a compact tool to couple with your torque wrench, 2 Unique makes a very good one.

My late father had a saying about that kind of fit; a derisive “Bend to fit, paint to match.”

Truth is, 30 ft. lbs. is not a lot. A strong man could just about do that bare-handed. With a wrench, you can deliver 30 ft. lbs. before you realize it. On the other hand, 80 ft. lbs. is getting close to the limits of aluminum. Use a torque wrench to test these limits for yourself.

Here’s the procedure for the non-torque wrench set. Use a regular ratchet wrench. Spin the barrel nut into place by hand. Do the tighten-loosen-tighten-loosen dance. When you tighten it the final time, do so by hand, noting where the nut stops. Now, put some muscle to it with the wrench. Can you get the nut to line up using the additional torque provided by the wrench? If you can, then you are within the 30-80 ft. lbs. range.

However, if the teeth still don’t line up and you must shift from muscling the wrench to putting a bit of body weight on it, you’ve likely exceeded 80 ft. lbs. You need to start over, either with a new barrel nut, shims or face-dressing.

REMAINING DETAILS

From here, you can either install the standard handguards or jump ahead to the handguard chapter to learn how to install aftermarket products. However, you may not be happy with the accuracy a plug-in barrel installation delivers. Put your accuracy expectations on hold and let’s delve into the reasons why rifles might not be accurate.

The barrel extension slides into the receiver up to the collar, and rests against the front flange of the upper receiver. Sounds simple, what could go wrong? First, is the extension a tight fit in the upper? Second, are the flange and the collar both axial and perpendicular to the bore? If not, then you could have a curable — or incurable, albeit minor accuracy — problem. First, the extension fit.

This is from a pair of barrel blocks. A “one size fits two” barrel diameter usually means it doesn’t fit any of them very well.

The barrel extension is a simple cylinder, 1.000 inches in diameter, and 1.000 inches in length. In a best-case scenario, the cylinder is 1.000 inch in diameter, and the bore in the upper receiver is 1.000 inch in diameter — perfect. But what if the dimensions aren’t perfect?

Let’s do some quick math. Suppose the barrel extension is only 0.999 inches in diameter. That means there is .001 inches of play. First of all, a cylinder inside of a cylinder cannot move the full distance of the measured difference, or play. That there is .001 inch difference between the two diameters does not mean the interior cylinder can move that much. Students of three-dimensional geometry can calculate the movement such space permits, but it isn’t the full .001 inches.

Second, the barrel flange constrains movement in the receiver. Despite this constraint, there is some movement and unwanted vibration. How to fix this? Well, there are ways, but you won’t like them, and they are to be done only when you are trying to wring the last quarter-MOA out of an already accurate rifle or components.

The first, and easiest way, is to use Loctite. Apply it liberally in a thick layer. Red, dark green, any of the strong ones will do. Avoid the wicking types. You need it to fill the gap between the barrel extension and the receiver, nothing else.

Make sure everything is clean and dry. Do this after you have determined the correct barrel nut and receiver-to-barrel flange parts. That is, if you need shims, you must know that before you start applying Loctite. Oil the threads of the upper receiver and the barrel nut. Apply a thorough coating of Loctite to the barrel extension and insert it into the receiver. Wipe off all Loctite that has oozed to the exterior. Install and bring to full torque the barrel nut. Remove the assembly from whatever holding fixture you have it in, and wipe all the excess Loctite from the interior of the receiver. Check one more time that the barrel nut is correctly timed, and set the assembly aside for at least two or three days. You want the Loctite to fully cure. The Loctite will now have filled the gap between barrel extension and upper receiver. You have decreased or eliminated the potential wobble.

If you want to remove the barrel, heat is your friend. Loctite degrades at 425 degrees Fahrenheit, and it will produce smoke while doing so. Once you’ve “burned out” the Loctite, you can wrestle the barrel out of the receiver.

The second approach isn’t so permanent, but can be more fussy. You simply wrap the barrel extension with steel foil, to fill the gap. You’ll need steel (not aluminum) foil the thickness of which is on-par with the aluminum foil you use in cooking. Use a single wrap, making sure it stays in place as you plug the barrel into the upper receiver. Once wrapped and inserted, potential wobble in the fit should have been reduced or eliminated. How much improvement can you expect? We’re talking fractions of an MOA here. If you have a rifle that will only shoot 3-4 inches at 100 yards, there are a lot of other things you need to be looking at to make groups smaller, including your own skill level.

A foil-wrapped barrel extension will be able to trim half or a quarter of an MOA off of an already accurate rifle. If your gun is not accurate, then foil wrapping is a waste of time. Wrestling with foil installation on a rifle that currently does its best at 3.5 MOA can wind up being a frustrating waste.

One last aspect of accuracy that you can take control of is the squareness of the upper receiver barrel ring. If the front edge of the ring is not square, the barrel will bolt down only onto the high spot, and you will be inducing tipping into the barrel fit. It won’t tip much, if at all, because of the fit of the extension shank to the upper, as we discussed above. But the tendency will be there and, at the very least, the unwanted added vibrations will cause problems. Also, you can experience a zero wander as the rifle heats up, since aluminum and steel expand at different rates.

How to solve this problem? Use a receiver squaring reamer from Brownells. The facing tool has a smooth cylindrical shank that rides inside of the upper receiver. On it, at the correct diameter, are cutting teeth. Use this tool to make delicate, light cuts. You are not looking to remove the entire face of the receiver down to bare metal. All you want to do is dress down the high spots, or correct a slightly off-square face. So, unless your receiver is way out of spec, use the cutter to simply clean up the face of the ring, which usually entails not much more than three-quarters of the circumference. It just needs to be smooth and square, enough to lock the barrel into place. If you cut more, you will be cutting below the hardened layer created by the anodizing, exposing soft aluminum to the barrel collar. That in itself is probably not a bad thing, but it goes against my grain to just cut it all off. If you want to, go ahead, but don’t blame me if it causes problems.

Correcting feed ramp problems is easy. It just takes nerve, a steady hand and a power tool.

One last detail on the face reaming. If you have already tried to fit the barrel nut, and had to do some work to get it properly timed, congratulations; your face-reaming/dressing just changed that. Remember, a shim of .001-inch thickness adjusts the barrel nut timing by one-third of a tooth. You just took metal off of the face of the receiver, where the barrel bears against it. How much? We don’t know, because every fitting job is different. And, you only took metal off of part of the circumference. So, was it .001 inches you took off the top? .002 inches? Unless you have very precise measuring tools, there’s no way to know for sure. But odds are you will find that the barrel nut now has to be re-timed. If you didn’t time it before, then you won’t have to do it all over again, just this once after dressing.

Lastly, a timed barrel nut on one barrel will not necessarily be a timed barrel nut on the next. Each fitting is unique to a receiver, barrel and nut.

ACCURACY

It seems that in some circles it is taken as a birthright that a personally owned AR-15 be a sub-MOA rifle. That many are, or can be, is clear. But not every rifle makes the grade. What does it take to up the odds?

First, get a quality barrel. A barrel with no pedigree, no name and bought at the gun show for cheap is unlikely to deliver sub-MOA groups. Second, fit it properly to the upper receiver, with a squared front ring and a properly timed and torque barrel nut. Third, feed it proper ammo (to match the twist rate, among other details). And lastly, be sure your shooting skills enable you to shoot sub-MOA

The military acceptance methodology is not an MOA measurement. Instead, it is a more statistically valid method, but one that is a royal pain in the butt to use. The method, in short, goes like this: the government fires a test group, out of a sample rifle, with known ammunition and pulls the target. The target is measured, and the geometric center of the group is determined. Then, each shot is measured to determine its distance from that center point. The mean distance, or average, is computed. If the rifle or ammo being tested has produced a mean average for each shot that is less than the stated, accepted value, it passes.

Does the government care if the accuracy is a lot better, just barely improved, or not at all? Nope. Remember, “The minimum becomes the maximum.” As long as it passes, it goes into inventory.

Here are the corrected feedramps. This will work just fine for years to come. I know, I did it the first time back in about 1988.

Now, that doesn’t stop some enterprising unit or individual from scrutinizing the tests and finding the production lots of ammunition that have produced the smallest groups. That’s one way to gain an advantage in competition.

Generally speaking, the allowable accuracy level for government work is around 3.5 MOA. That’s horrible, you say? Perhaps, but a 3 MOA dispersion nets you an 18-inch group at 300 yards. Since a person measures roughly that across the shoulders, that means a center hold at 300 yards nets you a hit on the bad guy.

As the saying goes, “Good enough for government work.”

The result of an overly long (heavy) bullet in a slow twist. The top is match heavy bullet ammo in a ¹⁄₁₂-twist barrel. Below, a ¹⁄₉-inch twist barrel.

BARREL BREAK-IN

How do you treat your new barrel? There’s a very strong feeling in some circles that you shoot once, then clean once, to ease a new barrel in. On a very expensive precision barrel, I can see giving it a try. However, having done so and seeing nothing for my efforts, I’m a lot less interested in such processes. I have two approaches, depending on the barrel quality or provenance.

Basic “blaster” barrels get no help. These are the ones you buy from the catalog on price — the cheapest rifled tube you can find in supply catalogs. You check headspace, plug it on, make sure everything is straight and get shooting. It gets cleaned when it gets cleaned. But doesn’t that hurt accuracy? I’ve done the exact process I’ve outlined and taken a new barrel to a five-day class. I’ve handed the newly barreled rifle out as a loaner while I fix students rifles, jumping in to get some practice when there is nothing that needs fixing, and ending the week hosing the 300 meter pop-ups. Somewhere between 500 and 1000 rounds — with no cleaning except chamber scrubbing to keep it running — and I’m still going one-for-one on the pop-ups, out to 300 meters.

Barrels just don’t need much care.

On the expensive, precision-accuracy barrels, I’ll be a little more forgiving. And the care comes as I tune the rifle. A precision rifle is going to have optics, and optics have to be zeroed. The so-called “break in” for an expensive barrel goes like this: Inspect, check headspace, install. Test-fire to zero iron sights, and use a patch with copper solvent on the bore. How much it fouls will determine how much care I give it. Does the bore clean up fast? Then it gets little or no care. Does it foul a lot? Then I’ll scrub the bore clean, in between groups to check the iron sight zero.

The front of M4-ramped receivers usually have a stamp, an “M4” to indicate their status.

Then I repeat that process while I zero the optics.

If it doesn’t foul much, the fouling cleans easily or decreases quickly as the bore gets broken in, then once I have the irons and the optics zeroed I don’t give the bore any more thought other than general cleaning when I’m done shooting. At that time, I’ll punch the bore with a copper-solvent patch, brush and dry, but only as a basic clean. No more.

The beauty of an expensive barrel is that the processes that make it more accurate are often the very same that make it easy to clean. Precision reamed and honed barrels, especially hand-lapped ones, have very smooth surfaces and stay clean.

ALIGNMENT, CLEANING

One detail that is important, if you are going to clean the bore, is to use a bore alignment, or guide tube. I cover this later in more detail, but it bears a reminder here; pushing rods through bores bend the rod. The rod will rub against the bore, and this can be bad for accuracy. So, if you push a rod, use a rod guide inside your upper receiver.

M4 RAMPS

I have this here because while it is a detail found (or not found) on the upper, if you have a problem, the barrel will be the likely source, thus the correction needs to be taken care of now.

This takes a bit of explanation. The original design of feed ramps were cut in the barrel extension from the magazine to the barrel. The front face of the receiver is simply a flat wall. Each round, as it strips forward out of the magazine, cams up so the tip strikes the feed ramp, and not the receiver wall. In the semi-auto rifle, and in the early M16A1s, there was no problem. Everything worked as designed.

By the late 1980s, however, there was a problem. The government had switched from the M193 to the M885 round. Colt was developing the M4. What Colt found was, when using the M855 round in the M4 on full-auto fire, the feeding became less consistent, and sometimes the tip of a round would strike the receiver wall. That would bring things to a halt, and also stub the bullet back into its case.

Taking the front sight off allows you to install the barrel nut shim intact, making the process easier.

So, Colt made the M4 receiver, so marked on the front, above the gas tube hole. The M4 receiver feed ramps are cut at a steeper angle and, as a result, extend down into the receiver wall. The barrels also had to be modified. This can lead to a rare but odd situation; barrel and receiver mismatch. For the purposes of this chapter, we’ll call the new one the M4, and the old one the AR. We have four combinations here:

AR barrel and AR receiver

M4 barrel and AR receiver

M4 barrel and M4 receiver

AR barrel and M4 receiver

The only one that is problematic is the last one, AR barrel with a M4 receiver. AR/AR is the original, and it works. M4/AR has the feed ramps steeper, but they do not overhang the receiver ramps (there aren’t any) and no problem. M4/M4 is clearly correct.

An AR barrel in a M4 receiver, however, has steeper feed ramps cut into the receiver wall, with less-steep ramps cut into the barrel extension. (We’ll overlook for the moment that the front sight is probably also a problem, but that’s a different chapter.) The result is that the ramps in the M4 receiver have an overhang from the barrel extension of the AR barrel. A bullet can catch in there and stop the cycle. No, this is not theoretical. I saw it in a recent class, and we had to correct it.

Colt is the gold standard when it comes to proper leade and markings on barrels. The code here means this is a chrome-lined barrel, has been magnetic-particle inspected and has a 5.56 leade with a ¹⁄₇-inch twist.

Before we proceed, you must be familiar with the front sight height considerations between AR carbine and M4 barrels. If your rifle is correctly zeroed, and the sight is not in the wrong place, then you can correct this problem back at the feed ramps.

If, however, you find you have a non-“F” marked front sight housing, and you can’t easily zero your rifle, the correct solution is to change barrels. Or re-cut the ramps and also replace the front sight assembly.

The process is, use a Dremel or similar tool with a narrow grinding tip or a carbide cutting tool. You can set it up in a mill if you are really, positively OCD and just have to. Or, you can do what every other gunsmith and armorer across the country does — hand-hold the Dremel, grinding the barrel extension to match the receiver ramps. That’s it; you cut the steel to match the aluminum.

Geissele makes the Reaction Rod, and if you are going to install more than one barrel in your life, you need to own one of these.

You can pull the barrel out of the receiver to do this. But the rest of us simply do the cutting or grinding with the barrel in the receiver. Once done, thoroughly hose out the grit with an aerosol cleaner, scrub the chamber, punch the bore with a solvent patch and then a dry patch, just to make sure you got all the grit.

That said, Colt wasn’t entirely correct that it was just a problem with M4s and M855 ammo. The problem did happen in semi-auto rifles and carbines, and not just with M855. I had it happen to one of my Frankenguns, back when Colt was still working on the M4 details. That rifle would occasionally stub in feeding. I looked at it, figuring I’d just buy a new upper receiver if it came to that, and went to work. I had to cut complete ramps of the M4 type, in both the steel and aluminum (which is why I used a carbide cutter) and it worked just fine. It still does.

But, when you order parts for your rifle to replace, rebuild or build from scratch, you want to pay attention to M4 ramps.

The Reaction Rod uses the locking lugs of the barrel extension to keep the barrel and receiver in place while you tighten the barrel nut.

This barrel nut can be tightened just a bit more to get correct timing. Unless, of course, you are already up to the 80 ft. lbs. of torque, which is the upper limit. Then you have to start over with a barrel nut shim.

TWIST RATES

When it comes to barrel twist rates, how fast is fast enough? The original Armalite AR-15 had a barrel with a twist of ¹⁄₁₄. That is, the rifling took 14 inches to complete one full rotation. While Arctic testing in extreme conditions, the government found that the ¹⁄₁₄ rate was marginal. If the air was as dense as it can be on a high-pressure day at 20 below zero, bullets become unstable.

The old canard about bullets tumbling in flight is wrong. I don’t care what someone tells you, or the basis of their experience, or where they were when it supposedly happened. It is wrong. So consider this your first lesson in avoiding bad advice; some people who should know better are wrong.

The government sped the twist rate up to ¹⁄₁₂, and there it remained until the A2 came along.

The next change happened when it came time to adopt the M16A2. The testing that had been done prior to adoption had utilized a barrel with a ¹⁄₇ twist. Not because it was best, but because it was fast enough to stabilize all the bullets the military was going to consider. You see, the longer a bullet is, the faster you have to spin it to generate sufficient gyroscopic stability.

With the adoption of the M16A2, and its ¹⁄₇ twist rate, things got complicated. Let’s get a few things out of the way first.

Here we have perfection. If you are between 30 and 80 ft. lbs., and your barrel nut looks like this, then you are done. Move on to the next step.

1/7 TOO FAST?

Yes, a ¹⁄₇ twist rate is too quick for some bullets. If you shoot ammo with the lighter hollowpoints, such as the varmint bullets, they may spin apart on their way to the target. This will likely not be a problem with 52 grain and heavier hollowpoints, and is not an issue at all with 55 FMJ.

The twist, while fast, will not harm accuracy. An accurate bullet will shoot to the level of its accuracy in a ¹⁄₇-twist barrel.

If you have torqued your barrel nut, and it stops here, you cannot apply more torque to get the nut to align or you will risk breaking things.

1/12 TOO SLOW?

Is ¹⁄₁₂ too pokey? Yes, for the military standard M855 bullet and anything longer or heavier. A ¹⁄₁₂ twist will throw a 62 grain M855 bullet sideways through a target at 25 yards. However, I have shot the Winchester 63-grain softpoint very accurately in ¹⁄₁₂-twist rate barrels. How? Simple. The M855 has a steel tip inside the core. This makes it longer than the blunt, round-nose, 63-grain softpoint from Winchester. The Winchester bullet is short enough that it can be stabilized (probably just barely) in a ¹⁄₁₂ barrel. I had a ¹⁄₁₂ pencil-barrel-equipped upper that shot those bullets into one hole at 100 yards. Well, at least until I wore it out.

So that means you use 55 FMJ and similarly weighted bullets in a ¹⁄₁₂ barrel, and anything heavier in a ¹⁄₇ barrel. That leaves the compromise, the 1.9. What’s up with that?

1/9, THE MIDDLE BEAR

The slam against the ¹⁄₉ barrel is that it isn’t mil-spec. But it can be accurate. Mathematically, a ¹⁄₉ barrel, firing the now standard heavyweight bullet of 75 or 77 grains, has the same stability as a 55 grain FMJ in a ¹⁄₁₂ barrel. Most of the shooters who pony up the money for the premium ammo (the 75 & 77 grains loads do not come cheap) would not go slumming with a ¹⁄₉ barrel. Their loss.

FASTER TWIST RATES

You’ll see barrels listed as ¹⁄₈. Those are usually premium match barrels, meant for a steady diet of nothing but 75-, 77- and even 80-grain bullets. Match shooters want X-ring accuracy out to 600 yards or more and will pay for a hand-lapped barrel. Those who are hurling even heavier bullets — 90 and 100 grains in the .223/5.56 — will opt for a ¹⁄6.5 barrel.

The catch here is case capacity. Heavy bullets like that are so long that if you loaded them so they would fit into the magazine, they would crowd out the powder you need to make velocity. So match shooters load them long — as long as they can, and still have the case neck hold the bullet properly. That requires them to load rounds one at a time, directly into the chamber.

Broken receivers. This is why the Reaction Rod was invented.

This is not a problem, because of the shooting times in matches. You see, while the timed and rapid fire segments of High Power competition call for 10 shots in 60 seconds, the long-range portion calls for a maximum rate of one shot per minute.

For each shot, the target is pulled down, the location marked and the target raised. The shooter notes the location of the hit, the target is pulled down, the hole pasted and then sent back up again. Repeat for the number of shots the scoring string calls for.

Unless you are heading off to shoot in NRA High Power, or off to Camp Perry, your choices are simple: a ¹⁄₁₂ for vanilla-plain 55 FMJ blasting, a ¹⁄₉ if you want to use heavier hunting bullets and a ¹⁄₇ for the heaviest bullets that will feed from a magazine. Beyond that, consult with the winning shooters in your club for advice on long-range target shooting.

CHAPTER 3
IRON SIGHTS

You need sights to hit what you’re shooting at. While some earnestly argue that point-shooting with a handgun still has validity in the modern world, no one, I mean no one, will argue the same for a rifle. Iron sights, as we call them, are the traditional post front and aperture rear. The older post-and-notch sights are customary on rifles such as the Winchester 94 or AK-47, but are absurd on an AR. That’s because they’re not as fast or accurate as aperture sights. The ’94 was a hunting rifle from an era when it wasn’t considered necessary to have more than one or maybe two quick follow-up shots. The AK-47 is basically a submachine gun on steroids, for which a notch-and-post open sight is just fine. We will be covering optical sights in a different chapter.

Here you can see the difference in height between the gas block and handguard. You must have the correct front sight or the height will be wrong and you’ll never get it sighted in.

Iron sights in the AR universe fall into a few camps; first, there is the A1 vs. A2 divide. Then there are folding vs. fixed. Other options include night sights, fiber optic sights and, when it comes to flat-top rifles with a rail running forward of the upper receiver, front sights that clamp to the rail or to the gas block.

Let’s start with A1 vs. A2, and work our way forward in time.

A1

In the beginning, there was the A1 sight, and it was good. The AR-15/M16 wasn’t viewed as anything other than a rifle for engaging distances spanning a couple of football fields. The A1 sight is not very adjustable. The front has a threaded post, but you only use it to establish a zero. Once that is done, you probably will not touch the front sight ever again. The rear has windage adjustments, but you need a tool, or the tip of a bullet, and some time to wrestle with it. The A1 also has a flip-rear set of apertures. The two apertures are the same size, and differ only in how high above the boreline they are drilled. The Army used the lower, shorter-range one for most work while the longer-range version, the one with the “L” marked on it, was employed for long-range shooting.

Properly zeroed, and fed the correct ammo, an AR-15 (the 20-inch rifle; remember, there were no carbines early on) with the L aperture up will cause bullet impact on the target when sighted with the top of the front sight post at 25 yards. That is the first intersection of the bullet traveling on a parabolic trajectory with your line of sight, which is a straight line. The barrel, since it is 2.6 inches below the line of sight, has to be tilted up (this is intentional) in order for that to happen. As a result, the bullet rises above, and does not come back down to the line of sight, until it has reached a distance of 385 meters.

Common military practice in aiming, at least since the advent of smokeless powder, was to hold your front sight on an enemy soldier’s belt buckle. This took advantage of the bullet rise over the line of sight, to extend ranges to where a soldier did not have to consider trajectory. With an M16, if you held on your opponent’s belt buckle, you could be sure of a hit out to 400 meters. (A hit below the belt buckle is still a hit in military usage.)

The problem with this ought to be clear. Smaller targets, at intermediate ranges, are not easily dealt with. This problem arose in World War I, when rifles zeroed for even greater distances caused bullets to impact a foot above the line of sight at 100 yards. From trench to trench, you could miss your opponent’s head (all he’d be showing) because your rifle hit high at that distance.

The lower unmarked aperture has a slightly less absurd trajectory, one in which the bullet will strike a smidge low at 25 yards (low to the point of aim) and then the second intersection is out at 250 meters.

None of this does you much good since the chance of needing your iron-sighted AR-15 at 350 meters are probably on-par with winning the lottery.

The front sight on a railed handguard. Assuming correct height, sighting in will be easy.

Typically, we use a 100-yard zero for all sighting in and zeroing of the AR, but you have to know what the sights were designed for, in order to get a solid handle on what you’re doing when you later establish your zero.

The A1 sight is solid, dependable, not easy to change and has remained the default sight for over twenty years.

A2

When it came time to upgrade the M16A1 in the early 1980s, the Army and the Marines did not agree. The Army was satisfied with the A1 sight system. (And planned to have the whole problem be moot when they replaced the M16 with yet another new system that was being tested. The Army is still testing a new system to replace the M16.) They simply wanted a new bullet. They needed something that would drill through the legions of body-armor-clad Soviet and Warsaw Pact troops they expected to be facing in Europe. That’s how we ended up with the M855, 62-grain “green tip” bullet. It came from NATO’s testing, and the bullet was called the SS-109.

While the Marines were interested in bullet design advances, what they really wanted was a rifle that posted good scores on the qualification range and allowed a Marine rifle company to deal with its problems. Specifically, the USMC was accustomed to working on a shoestring budget. An amphibious landing might find a wave of freshly landed Marines facing enemy resistance, with only the organic firepower they've brought with them. That meant no air support, no artillery, no offshore gunnery and no armor. Oh, those things might be available, but the Marines had learned that if you depended on it, and it wasn’t there, you were in a bad way.

A rifle company has to contend with multiple enemy machine gun positions. This process involves assigning a fire team on each one, placing accurate rifle fire on it, while another fire team (or three) maneuvered on its flanks. If that meant a team had to put rifle fire onto a position 400 or 500 meters out, then that’s what they had to do. And no, “close enough” won’t do in a situation like that.

This CMMG gas block comes with a rail on top and is a solid place to put a front sight.

So the Marines wanted a real rear sight, one that could be adjusted by the user on the fly, for range and windage.

Which is how we got the M16A2. The Army had to have the heavier bullet, which required a bore twist of ¹⁄₇ inches. The sights of the A2 are click-adjustable for range and windage. The system works because the rear sight parts are assembled in a moveable block. That block then raised or lowered when you rotated the elevation wheel underneath.

Unlike the flat plate of the A1 sight, the windage adjustment on the A2 is a big, graspable knob with which you can easily dial in the clicks you need to adjust for windage. Too easily, perhaps.

A1 ASSEMBLY

The A1 assembly is comprised of the A1 upper, rear sight aperture, screw, windage plate, detent ball and spring. The smallest of which — and the easiest to lose — is the retaining roll pin for the plate. You’ll need a small hammer and some oil to drift the pin. A bench vise, needle nose pliers and padded vise-grips are very useful.

Put the spring, edges down, into the recess in the upper receiver between the carry handle ears. Poke the screw through the left side and start screwing it into the aperture L. Set the aperture so that the stamped “L” faces you while you are threading the screw through. Once you have the aperture close to half-way across the screw, use the screw to lever the aperture down against the spring. While pressing the aperture down, poke the end of the screw through the hole on the right carry handle blade. The screw should be supported in both holes. Make sure the head of the sight screw is pressed up against the outside of the left-hand blade.

Lay the receiver down on the non-ejection port side. Put some tape on the edge of the windage plate and then clamp it in a vise. Be sure to keep the retaining pin hole vertical. Use a pair of needle nose pliers to hold the pin and, with a small hammer, tap it into the windage plate just enough to hold it in place. If you go too far you won’t get the plate over the screw shaft. If you don’t tap it in far enough, it will fall out as you handle the plate.

Midwest Industries (among many others) makes sights, and they know what height they have to be.

Now, put a drop of oil in the hole for the windage spring, press the spring in and place the detent ball on it. Note the location of the retaining pin hole in the end of the sight screw shaft. It is most useful if the hole is more-or-less vertical, compared to the axis of the bore. Now press the windage plate over the screw head, trapping the detent ball in the hole.

Use the padded vise-grips to clamp the plate in place. Turn the receiver upright and stand it in the bench on its lugs. Now tap the retaining pin into place. A drift punch is useful here, but if you have a steady hand you can do it with the hammer.

The trick is getting the retaining pin aligned with the hole in the correct screw. One way to accomplish this is with a short section of wire, just smaller than the holes involved — or a sharp, narrow scribe.

Once the retaining pin is in and flush on both sides, use the windage plate to adjust the aperture to mechanical zero, which is the center point of the carry handle. You’ll fine tune that when you get to the range.

A2 SIGHT

Unless damaged, there won’t be much need to assemble an A2 sight. Uppers come assembled, as do Backup Iron Sights (BUIS). However, knowing the parts involved and how to replace them if they become damaged, is necessary if rifles or carbines in departmental inventory have A2 rear sights.

Assembling the A2 sight body is the same process as installing sights on the A1 receiver, except there is less to hold on to. One difference is in the detent and ball for the windage knob. On the A1, the spring goes into the carry handle, on the A2, into the windage knob, which is a much thicker piece than the plate of the A1. That requires a tool of some kind. In fact, the A2 windage knob is meant to be finger-adjusted, unlike the A1.

Assembling the completed sight body into the upper receiver of the A2 is more involved. Secure the A2 upper in upright position on the bench. Place the elevation detent spring and detent into their tunnel. Put the elevation wheel upper and lower together, sliding them into the rectangular slot from the side. Press the detent down to clear the wheel. Be sure to place the wheels with the detent holes down, and the upper wheel so the numbers can be read upright.

Leave it standing for the moment. Pick up the rear sight assembly, and insert the tensioner spring and ball into the sight housing. Hold the detent in place and insert the threaded end of the sight housing into the elevation wheel. Without losing either of the detents, turn the wheel to capture and draw down the sight housing. Once the housing catches the elevation detent, the spring will not escape. Draw the housing down far enough so the tensioner ball is trapped behind the wing of the carry handle. Turn the elevation wheel until it bottoms out. Then bring it back up three clicks. This is the “mechanical zero.” The dimensions of the sight have been calculated to start 3 clicks up and all adjustments are made from there.

The A1 sight with flat plate. It requires the right tool to adjust.

Now rotate the upper half of the elevation wheel. It will turn without moving the lower half. Rotate it until the “³⁄₈” (on rifles) or the “³⁄₆” (on carbines) lines up with the index mark centered on the left side. Use a ¹⁄₁₆-inch Allen wrench to install the index screw. Once the index screw is in place, rotating the wheel turns both the upper and lower halves, changing the elevation of the rear sight.

The last step requires a special tool. Lay the receiver on its side (the left is usually easier). Push the spring in from underneath and use a special slotted sight tool (available from Brownells, #080-000-079) to compress the spring. Place the roll pin in the hole and tap it into place. If you lack a vise or fixture to hold the upper, (we almost all do) this is the time to ask for an assistant to hold the receiver in place (keeping the spring compressed) while you drift in the roll pin. In a pinch, you can use a closely fitting screwdriver to compress the spring. However, as with all such expedients, if something goes wrong you could end up losing parts, scratching the rifle or stabbing yourself with the screwdriver. If you’re going to do this more than once or twice, invest in the proper tool.

The big advantage of the A2 is its adjustability. However, that advantage brings with it many more parts and the possibility of mischief. Bored, idle or unknowing personnel (gun club “wits,” your brother-in-law, etc.) can spin the windage knob back and forth.

When the “L” is visible, the sight is installed correctly and you are set up to shoot at long-range targets.

One way to make the A2 less prone to inadvertent adjustment is to either acquire a locking windage knob (available from Rock River) or drill and tap the knob. To drill and tap the knob, first remove it from the upper. Then, drill from the rear between two of the plunger detent depressions, on the arc between them. If you use one of the depressions as your drilling point, the screw will eventually (if you do this to enough rifles) fall right on the plunger when the rifle is zeroed. Then the locking screw will be depressing the plunger as it locks in place. It gets the job done, but isn’t the best solution. Drill in between instead.

You should also paint in the sight settings — something you should be doing with all the other essential parts you have attached to your rifle.

BUIS

Pronounced “Boo-iss,” backup iron sights are meant to be used if the optical sights you are using as your main aiming tool have broken. On the modern rifle, they typically are of the folding variety, which keeps them out of the way — and out of the line of sight. They can be had in a host of styles, but the rear fall into two main camps, while the front come in two other styles.

REAR BUIS

The rears can be had in a design that is low enough, when folded, to clear the optical scope you are using. If your optic is a red-dot sight without a tube and with no magnification, then how low the rear sight is, provided it is out of sight, is not an issue. You can have a rather bulky rear sight and it won’t matter.

If, however, you are using a traditional, magnifying optic sight, then the rear BUIS must clear it or they can’t be on the rifle at the same time.

An example of the wrong way to do this is the Colt M4 handle, which was meant simply to be a way to bolt iron sights to an M4 or an M16A4. The first red-dot sight (RDS) was issued with the carry handle. Problem was, there was no way to have them both on the rifle at the same time. What ended up happening was, the carry handle was stuffed in a rucksack, or left at the base, and the rifle went out on patrol with a RDS, a front sight and no rear.

Some makers, like PRI, build the front sight right into the gas block. It also folds to clear the way for optics.

That later was changed when Matec sight was fielded and issued. Now, we have no lack of low-clearance rear BUIS from which to choose. You simply have to pick one.

The clearance of the rear BUIS is not solely up to the sight maker. There is also the issue of how large the rear of the optic is and how high the mount puts it above the top rail. Typically, mount makers work hard to put the bore of the scope on the same axis as the line of sight for irons. That way you do not have to shift your cheek weld when moving from one to the other.

The A2 sight system has a large knob for windage (the big one in the center) and a knurled wheel for range/elevation (the one inside the housing). They are great for target use, but overly complex for combat applications.

However, scopes are getting bigger. A 1-inch diameter scope will have a rear bell that is larger than the scope, but small enough to clear almost all folding sights (with the exception of the A2-based ones). However, when you start moving up to the 30mm, 34mm and even 36mm scope tubes, you have problems. One thing is the rear bell will be larger in diameter than the tube itself — it has to be, mechanically and optically. So a 34mm scope, with a rear bell that works optically with the expensive scope you just bought, might not allow for any folding rear to fit underneath.

That’s life.

Mounting a rear BUIS is simple. They will all have a built-in rail-grabbing arrangement. Loosen the nut, bolt, lever, whatever, and fit the sight over the rail. Position it so the rear of the sight, when folded, does not hang over the rear edge of the upper receiver. If it does, it will be exposed to anything that wants to hook on it — and something will. By keeping it flush with the receiver there is less chance of damage. But if you move it forward, it becomes less useful optically as an aiming device. And it can conflict with your optic’s mount.

The rear BUIS and the scope mount have to co-exist on the upper rail. Some mounts, no problem. But others, problem. You will have to do some makeshift positioning to make sure that the following conditions are met:

The BUIS does not overhang the rear of the receiver.

The BUIS does not interfere with the position of the scope mount.

The scope can fit within the rings of the mount with proper eye relief.

The replacement carry handle for the flat-top rifles and carbines in military service.

Once you have all the parts in agreement, you need to lock down the BUIS. This is one instance where I have modified my previous “No Loctite” policy. A drop of blue Loctite on the threads of the BUIS bolt is a good thing. It will be subjected to a lot of vibration and a bit of the right Loctite can only help. Hand-tighten the bolt or screw with a regular Allen wrench (if it is that kind of head) or a properly fitting screwdriver. If you are using a torque wrench, 20-25 in. lbs. should be more than enough. Once it is tight, use a dab of paint to both lock and record its position.

FRONT BUIS

There’s one important thing you have to know when selecting a front BUIS. There are two heights for them: One is designed for the front rail of a free-float handguard. It is generally shorter than the one that is meant to go onto the railed gas block.

The choice is simple. If you have a free-float handguard, and are putting the sight there, you need a “handguard height sight.” If you are using a low-profile gas block, with a rail on top of it, you need a “gas block height” front BUIS.

Otherwise your front sight height will be wildly wrong, and you will be unable to zero your rifle.

CHAPTER 4
STOCKS

Without a good stock on your rifle, you basically have a handgun. And while ARs can be handguns — the ever-popular AR pistols — we’ll cover them later. First here’s a look at AR-15 stock types and how they get replaced or upgraded.

Start by removing the stock from a standard A1 or A2 rifle. Why? First, because you are going to be taking the fixed stock off of a rifle (or carbine) so you can install a telestock. Second, you should know how the various parts work in the rifle, and not be limited just to the telestock layout. And finally, there are differences between the two that are important to know so you don’t find yourself in a predicament in the future.

Make sure the rifle is unloaded and remove the upper from the lower. With the fixed-stock lower in hand, put your thumb over the end of the buffer tube. Use a small screwdriver to depress the buffer retainer. Once you push the retainer down far enough, the buffer will want to pop out. Control it until you can get a hold of it, and then pull the buffer and spring out of the tube. Set them aside someplace safe because you will not be using them with the telestock.

Keep the safety on and, using a medium or large flat-blade screwdriver, unscrew the top screw in the buttplate. The lower screw only serves to hold the sling swivel in place so you can ignore it for now. The top screw has a hole drilled through it; this is a drain hole. If your rifle has gotten dunked, the water trapped in the buffer tube will not otherwise drain out and will impede proper function should you fire it. Water is an incompressible substance. Lacking that drain hole the moving buffer will pump the air out of the tube and the water will bring it to an immediate stop. You’ll have a short-stroke on that shot and each one after until the water is out.

As you unscrew the top screw, the stock will slowly move away from the receiver. That is because the rear takedown plunger spring is pushing on it. The stock holds the spring in place, so when you loosen the stock, the spring pushes on it. Take care to let the stock move back straight. If you let it spin around the tube, the stock will launch the spring and you’ll probably be ordering a replacement. Not fun, and you know how I know this.

This buffer retainer was not installed correctly. The buffer tube wasn’t screwed in far enough, just one more thread was needed.

Remove the screw once it’s free and pull the stock off the tube. The plunger might want to fall out and get lost, so remove it as well. If you don’t do that, the rear takedown pin can become loose and fall out. To save headaches remove everything and set the small parts aside. You’ll need them later.

As you talk to the various factions of the AR cognoscenti, sooner or later someone will claim a buffer tube is really a receiver extension. It isn’t worth getting into fisticuffs with this type of person, but do anticipate that he will be correcting you on your terminology every other time he’s within earshot. Yes, the military manuals and Colt call it a receiver extension. The rest of the world calls it a buffer tube. Call it a buffer tube.

The result was the retainer went for a stroll, and ended up rattling around in the lower receiver until it found some mischief it could make.

Put a thumb over the buffer retainer. Hold the lower receiver and, with your other hand, wring the buffer tube loose. Then spin it off. Once the tube has moved by a couple of threads, it will have uncovered the spring-loaded retainer, which will pop out unless you’ve restrained it. Once you have the retainer and spring out, and the tube spun off, you now have a lower retainer that is ready for a new stock assembly.

A buffer with built-in springs can have some uses, but for the most part I’m with the mil-spec crowd here.

TELESTOCK BASICS

To install the telestock, you’ll need a castle nut wrench and a spring-loaded center punch. A regular punch and a hammer can also be used. Like the fabulously awful mil-spec barrel nut wrench, the typical and historical stamped-steel castle nut wrench is to be avoided. Instead, get one that is robustly machined — one that will work.

Pull the new telestock and its parts from the plastic bag in which it was shipped. Examine the buffer and spring. Note that they differ from the rifle buffer and spring. The telestock buffer is obviously different, it’s shorter and has only one flange. You cannot use the telestock buffer in a rifle tube, nor the rifle buffer in a telestock assembly.

The telestock buffer tube has a spline down the bottom, which is the guide rib for the sliding part of the stock. Inside the slot, on the spline, are a series of circular notches. These are the locations the telestock pin locks into, keeping it in place when you have adjusted it.

On the telestock tube are a nut and plate. In most instances, the nut (called the castle nut), is threaded on backwards. The plate is the extra gizmo you need to keep the takedown plunger and spring in place.

Spin the nut off and remove the plate. You can leave the stock on the tube if it is already there. If it isn’t, don’t bother putting it on yet. First check the fit of the tube. Insert the tube into the receiver by hand until it has almost covered half of the buffer retainer shaft. Adjust the tube so the spline is pointed down and eyeball the fit of the tube in the receiver. You want the tube to cover the rear third or so of the retainer hole, but not have the tube stock forward of the top ring of the receiver at the inside edge. If it protrudes there, it will interfere with the upper as you close the action in assembly. Traditionally, the telestock tube has been machined with the front face of the tube squared-off on a lathe. However, the better brands, and the later designs, have the front edge machined with the top edge cut back, leaving a protruding lip with which to catch the retainer without interfering with upper receiver fit.

A badly machined, imported castle nut, with insufficient threads to hold on tightly. No wonder this kept coming loose.

Here is a castle nut with properly machined threads.

If everything fits, you’re ready to get on with assembly. If you need to make it fit, you have two choices: File to fit or return for a different/better assembly.

Making it fit should be a simple — if not nerve-wracking — matter for your first-time operation. You’ll need a bench vise, a large flat file and a circular file. Remove the tube from the receiver. Carefully clamp (it is a hollow aluminum tube, after all) the buffer tube, open end up in the vise. Use your flat file to remove some aluminum with a few strokes. Re-install the tube in the receiver and check the fit. It is as simple as filing until the upper clears the top edge of the tube. Then, once it clears, use the circular file to blend the bottom edge of the tube to the contour of the receiver. This does two things. It keeps you from having a shelf sticking in the way of the lower, and prevents having a sharp corner in the filed area, which could act as a stress riser. Once it fits, knock the sharp edges off that you have created by filing, and get to assembly. When you go to assemble, you can leave it white, use some aluminum finish or even spray paint to cover the bright aluminum.

In the old days, I occasionally had to do a bit more. After lining up the spline, and the top edge was dressed back so it fit, the bottom lip extended forward so much it held the retainer down too far to hold the buffer. I used a smaller circular file to put a small notch in the center of the bottom lip so the retainer had enough clearance. Having done this a few times in the past, it is interesting and amusing to see top-tier makers churning out buffer tubes with exactly those features — cut-back tops to clear the upper and a notched lip to give the retainer breathing room.

Now it’s time to install parts. Fair warning: the first few times you do this it will seem that you need three hands to accomplish the assembly. That’s not the case but it does take a bit of practice.

Spin the castle nut on with the large slots toward the buttplate. Screw it back onto the tube as far as it will go. Grasp the oval plate. Notice that it has a punched-in oval boss. That boss goes onto the tube, pointing toward the muzzle. Slide it all the way back on the tube until it is pushed up against the castle nut. Begin turning the tube into the receiver. Once it is on far enough that it won’t fall off, press the buffer retainer spring and retainer into their tunnel, holding them down with a thumb. Rotate the buffer tube until it traps the buffer retainer. Adjust the tube in or out until it holds the plunger in, clears the receiver ring and has the spline pointed down. Now install the rear takedown pin, push the plunger in and stuff the spring in behind it.

Push the retaining plate down the tube to the back of the receiver. Nestle the boss into the machined receiver recess as you use the plate to compress the retaining spring into the receiver. Once it is in place, hold it there while you hand-turn the castle nut down to the receiver to trap all the parts in place.

PWS makes a beautifully engineered castle nut and retainer plate, with a built-in ratchet system.

With the parts in place, inspect one more time to make sure everything lines up. Make sure the retainer is trapped, not just that the edge of the retainer is catching or merely being pinned down. Install the stock on the buffer tube. Turn the receiver upside down and use the stock as your gauge. Is the spline centered and orientated downward? If it’s tilted now it will surely be off when you tighten things. Get it straight.

You can tell the PWS buffer tube from others as it has flutes to lighten it.

Place the receiver on a clean, level bench with the muzzle direction to your right and the open top of the receiver away from you. The pistol grip and stock are your placeholders. Tighten the castle nut. Put some of your body weight into the castle nut wrench, but don’t make it “farmer tight.” Check one more time that the tele-slider is correctly aligned with the vertical axis of the receiver. If not, loosen the castle nut, tweak the stock back to vertical — or slightly past — and then tighten again. Why a bit past? The tightening action of the castle nut will pull the stock to vertical.

You aren’t done yet. The small notches on the castle nut (the ones pressed against the receiver plate) are there for you to stake the plate. Place your spring-loaded punch against the plate at the notch near the plate’s edge, pressing until the punch snaps and upsets the steel. Do this a few more times until you have a good bit of metal punched from the plate into the small notch. Repeat on a second notch. You will find that you can generally only reach two notches easily, which is plenty. The purpose of staking is to keep the castle nut from unscrewing when you shoot. The vibrations of shooting can loosen the nut.

PWS took the extra steps to capture the buffer retainer, clear the upper receiver, and extended it to be a crash pad for carrier tilt in piston guns.

Generally speaking, I am against the use of Loctite at the castle nut. You don’t need it and it makes disassembly harder. However, there are exceptions. Some receiver end plates are made of hardened steel, particularly the ones with added loops for sling attachments. If the plate is too hard to stake, then you have to loosen the castle nut, squirt a bit of degreasing aerosol into the uncovered thread area and dribble a few drops of blue Loctite into the gap. Dab the Loctite into the gap between the castle nut and the receiver plate, then tighten and let the stuff wick into the threads and gap between plate and nut.

The Vltor EMOD, with its built-in storage compartment.

There’s one new receiver plate/castle nut assembly that doesn’t require staking. Primary Weapon Systems has designed one with a built-in ratchet lever. The castle nut has 124 notches (they counted them, I refuse to do that, so I’ll take their word for it) and the notches catch on the ratchet. The ratchet notch has a built-in negative angle, so you can easily tighten, but the ratchet resists loosening. If you want to take it off, you have to use a small screwdriver or other lever to pull the ratchet out of engagement, otherwise it won’t let go.

BUFFERS & SPRINGS

The subject of buffers has been one of continuing confusion for some years now. The use of buffers in rifles, in particular ARs with A1 or A2 stock assemblies, is simple. It’s Hobson’s choice — use the originals, because they haven’t changed and don’t need to be. The rifle buffer is the longer, two-flanged one. The rifle spring is the one with 41 to 43 coils. (Yes, you can, and should, count them, just so you know for sure and know what they look like.)

When it comes to rifle buffers and the spring, more is not better. You do not want a heavier buffer, and you do not need a longer or stronger spring. Regular readers of mine know the record: a rifle we encountered in a class that had an “extra strong” spring that was so strong the rifle would not work. The spring had no less than 50 coils!

Carbine buffers have one rim, are shorter in length, with recoil springs sporting 37 to 39 coils. Despite the buffer being lighter, and the spring being shorter, they are correct for use in telestock tubes. Actually, they work pretty well ... when they work. When they don’t work, you need to tend to them. Carbines, unlike rifles, can benefit from some buffer improvements.

The buffer in both rifles and carbines is built as a dead-blow hammer. The weights inside are meant to rattle back and forth. When the bolt-carrier assembly closes, the carrier strikes the rear of the barrel extension. Steel-on-steel is a near-perfect elastic collision, and the result is a bouncing carrier. In semi-auto fire this does not matter as it is done several eons before your finger can press the trigger again. However, in full-auto fire, the autosear can release the hammer, bouncing the carrier as the hammer falls. If the hammer happens to come forward when the carrier has bounced, and is far enough back (it doesn’t take much), the bottom edge of the carrier prevents the hammer from contacting the firing pin. The result is the hammer resting on the firing pin with a loaded round in the chamber.

I had this happen in a class a few years ago. A Deputy from a nearby county arrived in our class (he wasn’t a student) with a malfunctioning select-fire SBR carbine. He had driven over from two counties away because his issued duty carbine was malfunctioning. After a brief description of the problem, I had him load and fire into the backstop. Sure enough, his rifle stopped. We opened it up, and yes, the hammer was forward, and there was a live round in the chamber. I pulled out the buffer weight (standard carbine) and replaced it with an H3 marked buffer. He then did three, full-mag dumps in full auto. Relieved, and with a grin on his face, he thanked me effusively, then pulled a carton of departmental-issue ammo out of his trunk and tossed it into the back of my pickup truck. Problem solved, tool fixed, and troubled mind relieved. That was worth a carton of ammo that the county had supplied to him for practice. His explanation was, “I would have shot up more than that trying to fix it on my own. You saved the county that much of my time by fixing it right away and getting me back on patrol.”

This was the kind of thing we had to do (back in the good ol' days) to get our faces properly behind a scope clamped onto the carry handle.

So, the weights inside are held to the rear of the carrier by inertia as the carrier goes forward, and then when the carrier stops, the weights move forward inside of the buffer an extra fraction of an inch and hit the inside front face of the carrier just as the carrier would be bouncing.

Again, for semi-auto work, this doesn’t matter. What does matter is that the weights are steel. When the carbine is a regular (more-or-less) 16-inch or so barreled upper, the steel weights work OK. However, if you shorten the barrel, install a suppressor, or do both, you have problems. Not bounce problems, but mass and inertia problems.

The shorter barrels need larger ports in order to deliver enough gas to the system in much shorter dwell time. This changes the timing and force of the gas arrival; many SBRs benefit from a heavier buffer. Buffers are made heavier at the manufacturer by substituting one or more of the steel weights with identically sized ones made of tungsten. One swapped weight is an “H” buffer, two swapped an H2 and all three an H3.

Here the buffer retainer is just barely being held in place. With time, this will most likely pop out and cause trouble.

Generally speaking, if you have buffers to try, use the heaviest in your carbine, with the following limits: Use the lightest-power ammo you typically use, and keep your AR dirty and dry. Use the heaviest buffer that will still lock open in those conditions, when the magazine is empty. The brass will be less abused and you will feel less recoil.

A quick aside, the Army, as they are wont to do, re-invented the wheel by upgrading buffers and congratulated themselves for being so clever. They added a new buffer to inventory, with instructions on where, when and in what rifle or carbine to install it. They call it the H6 buffer. It’s comprised of six weights, each half the size and thickness of the regular weights and fits inside of the buffer assembly. I have been told they are packed in there so that they do not move and do not act as a dead-blow hammer. Time will tell if that particular aspect induces malfunctions.

If you have an H3, you have a buffer that weighs the same as the H6, but has the dead-blow attribute — so don’t go changing unless higher command orders you. The H3 is better than the H6.

A special case is the pistol-caliber conversion, particularly the 9mm. Colt only ever made the AR in 9mm (no .40 or .45) so if you have a .40 or .45 you have something really off the beaten path. The Colt 9mm buffer is a special one, with extra weight added by means of a steel sleeve over the buffer body. The 9mm carbines and sub machine guns, or SMGs are not gas-operated, they are straight blowback, and need the extra mass to control timing and force of recoil. In a 9mm, the heavier the buffer, the better.

Top, a standard carbine buffer. Middle, a JP Enterprises competition lightweight buffer. Bottom, the original Armalite buffer, less than two ounces.

WHAT DO BUFFERS ACTUALLY WEIGH?

Buffer weight depends on the alloy for mass. The aluminum tube adds just about nothing to the mass.

Original, pre-M16 buffer* 1.9 ounces

Current, for all rifles 5.15 ounces

Carbine, standard 2.9 ounces

Carbine, “H” 3.8 ounces

Carbine, “H2” 4.7 ounces

Carbine, “H3” 5.6 ounces

Carbine, “H6”** 5.6 ounces

Colt 9mm Carbine 5.5 ounces

JP Enterprises low-mass competition rifle buffer 3.0 ounces

*For historical curiosity only. You’d never use this buffer, it is too light for any use.

** This is the Army, trying to re-invent the wheel and get credit for being clever.

You must use a carbine buffer in a carbine tube, and a rifle buffer in a rifle tube. And in carbines, my choice is to use the heaviest buffer that will lock the bolt back, with the softest ammo in common use.

A properly positioned buffer tube and a securely held buffer retainer. You want yours to look like this.

Buffers are made simply by lathe-turning rods of 6061 aluminum, anodizing, installing the weights and end cap. The synthetic cap keeps the buffer and tube from being hammered as the buffer weight bottoms out in the recoil stroke. The soft synthetic end cap is held in by means of a roll pin, and we have seen some of those pins work loose as of late. Check on your buffer occasionally just to make sure it isn’t one magazine away from disintegrating. (Trust me. That would be bad.)

While the relatively soft synthetic cap provides a bit of recoil relief, that didn’t keep people from improving it. The improvement comes in the form of a buffer, modified to have an internal or external spring on a shaft, which acts as a spring-loaded plunger. When the buffer bottoms out, the plunger soaks up more recoil while allowing the buffer mass to continue moving. This spreads the recoil impulse out over a longer period (measured in hundredths of a second, but still enough to notice) making the system seem softer in recoil. The total is the same, but the time is increased. Think of it as credit in monthly payments. The total cost is the same, but you get more time to deal with it.

The carbine using this buffer didn’t work so well. Once we swapped out this buffer for a proper one it worked just fine.

So, what are the drawbacks? For one, such buffers tend to be lighter than the heaviest ones available. They provide a decreased recoil impulse when the system bottoms out, but do so with more velocity than they would have had with a heavier buffer. If the rod bends, or the spring wears or breaks, the advantage is lost. And they cost more than the standard and heavy buffers. Still, they do work. If you can feel the difference and are willing to pay the price, then go for it.

BOUNCING SPRINGS

The buffer spring is full-diameter — it fills the aluminum tube in which it rests. Attached to it is a hard plastic stock. When the gun is fired, the cycling spring rubs against the tube, transmitting noise directly to your jawbone. One of the mechanisms of hearing is bone conduction. You hear things in part because your bones, being hard mineral structures, conduct sound relatively well. That’s why ear plugs do not offer as much protection as over-the-ear muffs do. The muffs cover some of the bone that would be conducting noise.

Buffers for carbines are marked as to their weight, with a stamping on the front face.

Inspect your buffer. This one gave up the ghost in the rifle and had to be wrestled out.

Well, the buffer tube conducts the noise directly to your jaw, and then to your ear. Some find the noise noticeable, even annoying. Others don’t notice it or their face offers enough dampening to keep bone conduction to a minimum. Yes, having a fat face can protect your hearing.

John Paul of JP Enterprises solved that problem by building a recoil spring along the lines of the spring-loaded buffer, but more. The entire recoil spring assembly is a captured system with weights and spring on a central rod. You do not need a buffer with this design as it has its own buffer mass built in. Installation is easy. Open the upper and lower. Pull out the standard buffer and spring. Install the JP system with the weights to the front. Close, reload and continue.

Paul, not being one to leave things alone, improved it to the v.2.0 system, offering a .308 version.

The big advantage is no spring boing. The spring rides on its own central rod, thus it cannot contact the buffer tube — nor rub against it.

BUFFER PROBLEMS

Buffers may be durable but they do not last as long as carriers. The biggest problem is cheaply made or counterfeit buffers. I’ve seen them with mangled plastic backs made out of a cheap substitute polymer. (How can you get cheaper than plastic? They manage somehow.) For a while back in the 1980s and 1990s, we saw plastic molded buffers that were filled with lead shot. Those were awful. If you have one in a Colt (Colt even made and used them for a while, but not on military rifles), replace it and do not regret changing a factory-original setup. On this score Colt did wrong, and you should not suffer as a result.

The Rock River Operator stock is solid and comfortable.

One really egregious buffer I saw a while ago was made from lathe-turned heads (the nailhead-looking part) married to tubing. It probably would have worked fine except that the maker was even cheaper than cheap and didn’t use seamless tubing. The tube split on the seam, driving the plastic part into the buffer body until the weights inside stopped it. We had to wrestle that one out of the stock because it was binding on the spring.

Then there are those that are lathe-turned, but not anodized. The faces that rest against the carrier on these get chewed to pieces in short order.

And who can forget the particularly craptastic buffers that had a single steel weight inside. Yes, it clacked back and forth when you shook it, and caused the most spectacular malfunctions.

A QUICK CHECK

To see if your rifle has the proper parts, unload, open it up, and pull the buffer and spring out. Shake the buffer. Do you hear the weights clacking back and forth? Good. If you hear shot rustling around in there replace the buffer. Count the coils. 37 to 39 for carbines, 41 to 43 for rifles.

MISMATCH PROBLEMS

What happens if you put a rifle setup into a carbine tube and vice-versa? On the one hand nothing; and on the other, lots of bad things. The rifle buffer and its spring will not fit into the telestock carbine buffer tube. You can’t get them in far enough past the retaining plunger to close the upper and lower. To save you from yourself, they are just too big.

Here is a carbine buffer, disassembled next to an intact one. You can see the three weights and their fiber-synthetic pads.

Unfortunately, the carbine weight and spring will fit very nicely inside of the rifle buffer tube. That’s not good because the carbine buffer will travel too deeply into the tube when you fire. This allows the carrier to travel further back. It will stop only when the carrier key bangs against the edge of the buffer tube or the ring of the lower receiver into which the buffer tube is screwed.

If you are lucky, the only damage will be gas key screws getting sheared off, causing the rifle to stop working. If the screws do not shear, the key will hammer into the receiver until it breaks the receiver. Ouch. The lower is the part with the serial number; therefore, you will be replacing it with one that has a different serial number, and in some jurisdictions that can be a problem.

MISMATCH NON-ISSUES

Can you swap upper and lower assemblies? This is a question that comes up in classes. The short answer is yes. You can put a fully-assembled 20-inch rifle upper onto a lower receiver that has a carbine telestock on it. You do not change anything in the lower.

I have been in correspondence with an acquaintance in the military, and it seems his unit is doing just that. They placed an order for a truckload of complete telestock assemblies, and are in the process of swapping fixed stocks off of M16A2, A3 and A4s, replacing them with telestocks. Yes, the resulting rifle still has a 20-inch barrel, but at least the stocks can be adjusted for use with body armor — and they are a little bit handier in use.

You can also park a 16-inch carbine upper onto a rifle-stock lower. Colt did exactly this back in one of the so-called assault weapon ban panics, and it turned out to be a nice, handy, lightweight carbine.

The H is on the right, the H3 on the left, and in-between is one of the really bad plastic ones with lead shot. Avoid that one like the plague.

The gas system of the upper is tuned to deliver the correct amount of gas to the carrier, regardless of the barrel length. The buffer system is designed to deal with a carrier that is cycled with a certain amount of force regardless of the barrel length.

As long as the uppers and lowers involved are correctly assembled with the proper parts, you can swap uppers and lowers to your heart’s content.

Now, that guidance is engineering advice. If there are legal reasons you cannot swap uppers and lowers, well then don’t do it.

When the US government was sending surplus M16A1 rifles to police departments, some agencies did just that. They took lightweight rifles with 20-inch barrels, removed the fixed stock and all its parts, and replaced them with telestock assemblies. This allowed officers to fit the now shorter rifles into the overhead racks of their vehicles — and then get them out in an emergency without a crowbar and two assistants.

The departments that were more flush with cash swapped the uppers as well, and simply put carbine-length (or shorter machine guns for which there is no minimum barrel length) uppers on the lowers, swapped the stocks and issued them. They also secured all the parts — uppers, fixed stocks, and the auto sear — locking them in the arms room. If the government ever wants the rifles back, they’ll want them returned in the same configuration in which they were shipped. Understandable wear is OK, but modified and rebuilt to non-government standards? No, you aren’t shipping that back.

Get a good castle nut wrench, something with three teeth to grab the nut slots with authority.

A front sling swivel can be as simple as a loop of braided stainless cable.

Make sure you keep your sling under control. Too much can be too much.

A loop of 550 cord, properly tied and sealed, makes a lightweight and compact sling attachment system.

SLING ATTACHMENT POINT METHOD FOR AR STOCKS

I’m a Neanderthal when it comes to slings. Sure, I learned the classic leather target sling, you know, where the thing is so tight that not only can you see your heartbeat in the scope, but your fingertips are turning blue as you aim. But I never had any use for it, since the competitions I shot in never called for it. Those contests even made the device difficult to use. So, for me a sling is simply a means of carrying a rifle, and to keep it off the ground while you use both hands for something else.

To that end, I have settled on a pretty simple sling system. The stock end is the easiest to describe, since it doesn’t involve any hardware.

Take a length of 550 cord, 2 feet is a start for fixed stocks, 18 inches for telestock. Loop it over four fingers, and tie a knot. Hold the loop at the top of the stock, while you run the tail ends over the other side and back up to the top. On the fixed stock, loop the ends so they are behind the bottom sling swivel. This way it can’t slide forward. Tie the ends in a knot behind the loop on top. Melt or glue the cord ends so they can’t come loose. The knot behind the loop keeps it from sliding off the back of the stock when you use it. Pull the knots as tight as humanly possible.

On the telestock, loop the ends down and through whatever slots, gaps or opening the maker of the stock provided, and back up to tie off just as you would with the fixed stock.

This is your rear sling swivel. With this approach, the sling comes off the top of the rifle, not the side or bottom. It is light, inexpensive and quiet. I can install it on any rifle in a matter of minutes, and take it off even faster. I can put it on a rifle for a class, and take it off when I’m done, without any permanent modifications to the rifle.

On the front, I take one of three approaches. The first is a loop of braided stainless steel wire/cable, secured in a circle with a cable pinch. I loop the wire though the front sight housing, and then back through itself so the loop is locked to the rifle, extended for the sling. A refinement of this is to add a length of cable cover, to reduce the wear on the sling. The advantage of this approach is that you can put a side-mounted sling on a bone-stock rifle or carbine, and then remove it when you’re done. If you arrive at a class where they’ll be using issued rifles, and you don’t want to screw around with a classic sling, this is the answer. You can have this loop in your gear, install it in a minute, and get to the class with something resembling modern equipment.

The second is to tie a short section of 550 cord to the railed handguard and use that as the front sling loop. The advantage of this is that it is cheap and you can install it on a rifle you’ll be using for only a short while.

The last is to use a clamp-on sling swivel on a railed handguard. This can be a quick detach style. It’s easy to attach (requires a railed handguard) and you can place it right where you want a hand stop.

The sling itself is a simple nylon strap to get the rifle hanging where you need it. The strap allows you to sling the rifle behind, but not so loose that it dangles down around your waist or knees. Too much sling can be a problem. Not only can it let the rifle hang too low, or swing around too much, but it can get tangled up in the darndest things.

I am not a fan of single-point slings, and avoid them if I can. Now, if you do not want to experiment with 550 cord, then modern free-float handguards quite often incorporate QD sling sockets in the design. Also, modern stocks do this as well. It is easy enough to simply pick up a set of QD swivels, attach your sling, and plug them into the sockets. My recommendation for slings is, the simpler the better.

You can simply tie 550 cord to your free-float handguard.

Midwest Industries, among others, make a bolt-on sling swivel that also works as a hand-stop.

Want a top-mount sling on your fixed stock? This works and is cheap.

Those little circular holes in many stocks and forearm designs are the sockets for the QD sling system.

Visit your local hardward store and, for as little as $10, you can get enough material to make as many of these loops as you need to sling up all your ARs.

STOCK DESIGNS AND TUBE CONSTRAINTS

The rifle tube is the rifle tube, that’s it, there is no other. If you have a rifle tube your problems are zero. Telestock tubes, on the other hand, come in two sizes — military and commercial. Why? The military specs call for the tube to be made by means of forging. The aluminum bar from which it's made is pounded (forged) into the shape of a rod with a rib. The rod is then bored out, threaded, and the exterior profiled, while the rib is machined for the locking latch and detents. The profiling makes the tube walls as thin as possible, yet retains maximum strength. This reduces them below the diameter of the thread tops. If you look at a military-diameter tube you will see that the threads have been topped-off on the back end of the threaded portion.

The commercial tubes are made by means of extrusion. Heated bars of aluminum are forced through a die shaped like the telestock tube. They are then bored out and threaded. They are not profiled. These do not have the threads topped off.

The commercial tube is generally 1.17 inches in diameter, but can vary quite a bit, while the mil-spec tubes are 1.14 inches and are quite close to that dimension. If you have a commercial stock, it will rattle loosely on a military buffer tube. And unless you have a really big mallet, you are not going to get a military stock on a commercial tube.

You have to know which you have if you plan to replace the telestock slider and stock for one that has the features you want. A dial or digital calipers will quickly tell you which one you have.

Why the difference? Forging is expensive. The 7075-T6 alloy of which forgings are made add to the cost. 6061 aircraft aluminum extrudes beautifully; even if it is a bit gummy to machine. So if you want to save money making telestock assemblies use extruded 6061, and do not waste time and effort profiling the tubes down to 1.14 inches. Simply extrude to the final dimension of 1.17 inches, bore out, machine the rib trough and thread the ends.

The threads are the same for both as they have to fit into the lower receiver. That means that all the castle nuts, retaining plates, etc. will fit both types without a problem. Actually, if there is a problem, it isn’t because one is commercial and the other is mil-spec diameter.

The rifle buffer weight is longer, with two flanges, and won’t fit in the carbine tube nor allow the action to cycle.

REMOVING/INSTALLING TELESTOCKS ON THE BUFFER TUBE

The telestock slides on a rib in a slot with bored recesses. The original telestock had two positions — open or closed. As time went by, the number of recesses has increased, with six, even seven settings now available. The lever on the stock unlatches, allowing you to slide the stock forward and back. But how to remove it?

The small rib on the rear of the receiver is where the rear takedown spring and plunger reside.

Pivot the latch and slide the stock all the way back. Now, instead of causing it to pivot by depressing, grasp it in one hand and pull the whole thing away from the buffer tube. You will then have moved the post enough to clear the rear lip of the rib. The stock simply slides off the end.

Which stock should you use? That depends.

Are you after compact size, light weight, comfort in shooting or one with a cup holder to keep your coffee off the ground while you consult the map? (OK, a bit of a joke there, but only a bit. Stocks can be had that do almost anything.)

The lightest is the simple, ribbed M4 stock. Lighter still is the old retro XM177 CAR stock but only if you get the plastic one. The aluminum choice (which was the original type) is heavier than almost anything. Here you are on your own. The wedge-shaped Socom stock, or Crane stock, is very comfortable to shoot, but it is heavier and bulkier than the M4. You can have stocks with storage compartments in them — to store batteries or cleaning gear. There's even a stock that lets you secure a tourniquet to it.

As long as you are willing to put up with the weight, get what works for you.

STOCK ARRAY

Let’s look at a few stocks and see what kind of variety you have to select from.

ACE LTD. M4 SOCOM

If you want simple and straightforward this will do it. The design is simply a tube with a stock that is a reinforced buttplate. The place where you rest your face is covered with a foam tube. That’s it. Installation is simple and follows the same process that a telestock would. When installing the Ace, or any other telestock for that matter, you have a choice in end plates. The retaining plate for the telestock assembly also keeps the rear takedown spring and plunger captured in the receiver.

You can use a regular plate or one that has looped flanges for attaching a single-point sling. The plates are the same regardless of commercial or military-diameter tube. The M4 Socom is adjustable, with two different sized versions available. There are 7.5–9.5-inch and 9.5–11.5-inch lengths. If you want a compact, simple and durable stock, go ACE M4.

SLIDERS

No, not small burgers, but the part of the telestock assembly that actually slides back and forth. You can have sliders in an amazing array of colors, shapes, weights and intents. They all slide onto the buffer tube, and once you have determined military or commercial diameter — assuming the stock you want is available in that diameter — then it is simply a matter of taste, comfort, the weight you are willing to pack, and the extra features you simply must have.

DANIEL DEFENSE

Daniel Defense uses a glass-fiber polymer for the body of their stock, which is over-molded with soft rubber for comfort. The cheekpiece area is wedge-shaped for a solid cheek weld, and has a non-slip but not hard-on-your-face rubber section. There are QD sling swivel sockets and slots for fitting a sling. The bottom of the stock has a connector, its toe serving as a support if you should happen to fall on it or use it to buttstroke a door, face or other object.

MAGPUL

Magpul was one of the first in the aftermarket stock segment and pretty much hit like a tsunami. You can have any of 11 different designs, some of which are telestock, and some fixed, in 10 different colors.

Me, I’m pretty much a stick in the mud, and use the MOE or the CTR. But I do have a rifle with a UBR and another with a PRS.

VLTOR

Vltor (ull-tor) makes three stocks — the ARM, which fits onto a fixed stock buffer tube, and the EMOD and IMOD, both of which go onto a telestock buffer tube. They all offer better ergonomics than the M4, with proper wedge-shaped profile and added storage compartments. You also have color choices, black, FDE and Foliage green.

The ARM has QD swivel sockets and sling slots. The EMOD and IMOD have only QD swivel sockets. Of course, if you are doing the 550 cord sling setup I use, there is plenty of room for that.

WILSON COMBAT

The Wilson Super-Stoc is reinforced polymer black that features two levers. One is the adjustment latch, which lets you slide it back and forth for length of pull. The second takes all the wobble out, making it feel like it is a solid stock, not a telestock slider. It has sling slots and QD swivel sockets.

ROCK RIVER OPERATOR

The RRA Operator stock, available both as the original and the A2, the latter for a fixed-stock rifle, is solid and comfortable. It has two QD swivel sockets on each side, with a slot for a sling or 550 cord. The storage compartment is underneath the buttplate. So you have a better chance of keeping things dry in there, slide the buttplate down, then weasel out the rubber o-ring sealed plugs to remove whatever you’ve stowed.

Some stock designs use non-standard buffers.

CHAPTER 5
BOLT, CARRIER AND HEADSPACE

The AR works like this. Incoming gas from the gas tube travels into the gas key, which directs it to the interior of the carrier. There the gas expands and cools, the force of expansion driving the system. Basically, what the gas does is treat the carrier like the remnants of a drinking straw. You know, you tear off one end, you put the open end of the straw in your mouth and you blow the remaining sleeve of paper at your annoying sibling.

The gas blows the carrier away from the chamber. In the wall of the carrier is a kidney-shaped slot. That slot holds the cam pin. When the carrier moves, it acts to rotate the bolt, using the cam pin as a lever, and once the bolt has been rotated open, the carrier hauls the bolt back away from the chamber.

To control gas flow and timing, the carrier has vent holes in its side, aimed at the ejection port cover. The bolt has three gas rings in its tail section, which act exactly like the piston rings in your car — controlling pressure and preventing leakage. In an interesting development, the gas in the expansion chamber not only pushes the carrier to the rear, but pushes the bolt forward, taking some load off the lugs, easing rotation and opening.

Now this is in the original, direct-impingement system, also known as DI. In the various piston systems, the piston rod pushes (or strikes, depending on the design) on the carrier, but that adds a bit of complexity. You see, the gas system pressurizes the carrier along its central axis. The piston pushes on the carrier off-center, and this leads to a phenomenon known as “carrier tilt.” The rod pushes on the carrier above its center of mass, so the carrier attempts to rotate, and that means the rear end of it tips down. This can lead to gouging of the buffer tube where it meets the lower receiver. Manufacturers deal with this using several methods. One is to make so-called skid pads on the bottom of the carrier to stop tilt and create a sliding motion before the carrier can tilt too much. Another is to extend the bottom lip of the buffer tube forward, to keep the tube under the tilting carrier rather than the threaded portion of the lower receiver, or the front edge of the buffer tube.

The carrier blows back, hauling the bolt with it. The bolt extracts the fired case, ejector tossing the case overboard. Once the carrier bottoms out in the buffer tube, the spring pushes it forward where the bolt gobbles up another round, chambers it, the carrier cam slot works its leverage on the cam pin, the bolt rotates closed and you’re ready to repeat.

That’s the system in a nutshell. Now, let’s look at the individual parts, starting with the carrier.

CARRIER BUILDING & INSPECTION

The carrier is a nearly indestructible piece of equipment. You can break it, but in so doing you’ve probably just blown up a rifle, and everything else on it is toast, too. I’ll take a bold stand here and say you cannot wear out a carrier. It has no accepted service life because it is not a wear part. And the only wear part on it, the gas key, can be replaced.

Carriers come in a variety of configurations, with said variations all having something to do with one of two areas: the lower rear hoop or the firing pin shoulder. Oh, you can find steel, aluminum and titanium carriers, lightened carriers, heavy carriers, and carriers plated with every other metal or alloy known to man, but we’ll get into those later. For now, we’ll just cover the common ones.

The bottom rear hoop provides the proper (as in originally designed) mass for the carrier, and it is the bearing shoulder that trips the auto-sear in full-auto or burst fire. As-is, there is nothing inherently bad about it. However, back in the early days when the first attempts at “assault weapon” control (and this was so long ago the pejorative term hadn’t even been thought of as a stick with which to beat us) were going on, Colt figured they would solve that problem by clipping the hoop. So, the semi-auto AR-15 carrier has a hoop shorter than those on an M16.

And a brief side note, the originals were all AR-15, even the select-fire ones. It was only when the Army, via the DoD, adopted it did the term M16 come into the parlance. So, if you happen to see a select-fire Stoner-system marked “AR-15,” it may well be an actual real one.

Modern manufacturing holds all parts to amazing tolerances. Well, the good ones do, and they cost more than the cheap import rubbish. They’re worth the extra cash.

This didn’t last long, and Colt added another change — the firing pin ramp. The select-fire carrier’s bottom ramp extends back almost to the rear of the firing pin. If the carrier is not fully closed, the hammer can’t reach the firing pin, instead striking the bottom shoulder of that ramp, preventing an out-of-battery discharge.

Alas, people who were doing a modification known as “follow-fire,” an attempt to illegally convert an AR-15 into a pseudo M16 (and no, I won’t tell you how it is done) found that shoulder useful. Useful in that if the rifle didn’t quite cooperate, it wouldn’t blow up.

So, Colt made three changes, one of which involved the carrier; they opened up the ramp so the retaining shoulder on the firing pin was exposed. They made the flange on the firing pin larger in diameter. And they cut a notch into the top corner of the hammer. Now, if the members of the “hold my beer and watch this” lot tried to make their mods, the hammer would catch its hook on the exposed firing pin flange and stop.

All this had the effect of making the full-auto carrier an object of myth, legend, rumor and gossip.

A quick discussion of legalities and the Bureau of Alcohol, Tobacco, Firearms and Explosives, or ATF. The ATF will not tell you how many M16 parts are OK to have in your AR-15. This is part discretion, and part recognition. The recognition part is that if they put a hard-and-fast number on it, the next day 100,000 experimenters will get to work. If they say, “You can have X number of M16 parts in your AR-15, and it is OK” then the experiments begin. And every iteration of parts will be tried, tried and tried again, until someone finds a way to put the magic number of M16 parts in a rifle, thereby generating legal full-auto fire.

Left, the lopped-off Colt carrier. Center, the Colt AR-15, and right, the M16 full-auto carrier.

The other is that by not setting a limit, if you have one, and you have a rifle that fires full-auto, they have the option of simply spanking or imprisoning you. Prosecutors love discretion, as it means their job is easier. Hey, it’s human nature.

This standard government position lead to the unintended consequence of a blizzard of letters arriving at the ATF tech section every year. You got a question? Write it up and send it in, and the ATF will answer. Unfortunately, being a government agency, they can’t simply have a wall rack of response letters, sort of a hard-copy FAQ. That would be too easy. No, each letter has to be read, handed to the answer committee and then a response typed up. The response always follows this format:

Top, the ramped firing pin shoulder that Colt made for a long time. Bottom, the shrouded firing pin shoulder on the M16 and other semi-auto carriers.

Thanking you for your inquiry.

Re-stating your question.

Responding to your question by quoting the relevant section of regulations or statute.

Reminding you that the important part of this situation is the exact wording of the statute.

Thanking you for your interest in the situation.

The response to a blizzard of questions on a single subject ends up being one of two things: the ATF admits the process is clumsy and annoying to all, or they change the regs.

In the case of the full-auto carrier in a semi-auto rifle, the ATF just told the manufacturers that they, the government, didn’t give a [fill in the blank] and to use whatever worked. That’s how you find full-auto carriers in rifles these days. Do not, I repeat, DO NOT write to the ATF, asking if the full-auto carrier in your AR you just bought is allowed. It is. The company that made it knew this. Such letters only do two things; bog down the letter process for other questions, and annoy the ATF.

And it can lead to other less-fortuitous outcomes.

A few years ago, an inventor came up with an idea. It was a rig to allow the disabled to shoot AR rifles. The arm brace was born. It was such a success that Sig bought it. And it was such a success that everyone had to have one. And far, far too many wrote to the ATF, asking, “Is this really allowed?” So many, in fact, that the agency had to sit down and take another look at the piece of gear they had approved. And they suddenly “discovered” that a lot of people were using it, people who were not disabled. And they changed their interpretation.

Now, I don’t think the re-interpretation would stand up in a court of law. However, no one is going to deliberately challenge it. Why? Because you have to have standing. “Standing” in the legal sense means you have been harmed by the law and can now challenge it. In this case, you can’t take the government to court on the arm brace issue, because you have not been harmed. You do not have standing. How do you get standing? You get arrested and charged under this interpretation.

Best outcome? You spend years, and a metric buttload of money, prove the interpretation wrong and get to live your life. You do not get a refund on your legal expenses, nor can you collect from the government. Worst outcome? The interpretation is proven correct, you still spend years and money, and then you go to jail.

I say thanks for nothing to all those who wrote letters, despite the fact that a copy of the approval letter from the ATF was enclosed with each arm brace.

But we have wandered far afield, and have to get back to the subject — carriers.

Your carrier will come out of the package either bare or with a key on top. And there isn’t a lot you can do to a carrier except inspect one important area, the bolt tunnel. Peer inside the front and you’ll see a hole bored down the center. That’s where the bolt will ride. The interior of the carrier is hard-chrome plated for wear and corrosion resistance. However, not all are the same. Look closely, and even use a light if you need. Do you see any circumferential marks? How about tool marks in the chrome plating? If you do, send it back and request another. Not that there is anything obnoxiously wrong with tool marks. But, what they will do is wear your bolt gas rings at an accelerated rate. The bolt cycles back and forth in the bore hole each time the rifle cycles. That means the rings slide along the shaft walls. If the tool marks are high enough, or sharp enough, they will wear the rings, and quickly.

The bolt has a rotating band that keeps the crud from getting in the way. This bolt isn’t even close to the dirtiest I’ve seen.

Gas rings come in trios. If the rings in your bolt are worn and need replacing, take care of all three. Don’t be cheap. Whatever savings you reaped by only replacing one or two will be quickly eaten up by the test-fire ammo you burn just to make sure.

The carrier will not wear to accommodate the bolt rings because it is hard-chrome plated. The chrome is so much harder than the rings, which will just be filed down by the toolmarks. I’ve seen rifles where the carrier was so rough that gas rings lasted about 500 rounds, and needed to be replaced when tested. Not that this is bad, but replacing rings twice on each case of ammo is a hassle, and you never know if they have worn too much until you either test them or the rifle starts malfunctioning.

The easiest way to solve the problem is exchange the carrier for one with a smooth interior. When you send it back, explain why, what it means, and who told you to do it.

I’ll be glad to take the hit.

GAS KEY

The key is the little spigot up on top of the carrier, the part that slips over the end of the gas tube, directing gas down to the carrier interior. Unless you drop it, the key is not a load-bearing element of the rifle design and not subject to impact. However, it must maintain a gas seal or your rifle won’t work well.

The quick check is this: hold the carrier in one hand. Grasp the key with your other hand. Try as hard as you might to move the key by wiggling it. If it moves at all, you must follow the proper process to make it tight. The proper process is to first remove it. Grab an Allen wrench and remove the screws that are there. If at all possible, have new ones to replace them. If you don’t, re-use the existing ones. But screws are cheap, so always have spares.

The tightening process is the same as the initial installation process.

Scrub the carrier and key clean. Use a clean, medium-grit stone, or a flat narrow file and some emery cloth, burnishing the slot in the carrier and the bottom of the key. You want them flat, smooth and clean. You don’t have to remove all the Parkerizing, just knock any high spots down. And clean any gunk out that might be there.

Degrease again. You want to apply some sort of fastening adhesive. The mil-spec calls for Permatex, a self-forming gasketing material. I’ve seen several different Permatex’s listed as correct, so the requirements are not particularly difficult to meet. Also, I have used both red Loctite and the dark green Shaft and Bearing Loctite to successfully seal the key.

Some will say that a sealant isn’t necessary. I won’t say they are wrong, but I will note that I have visited the Colt factory and, while I was there, watched the carrier assembler use Permatex and apply it to the carrier trough before torqueing down the key screws.

Clean, then smooth the parts where they bear on each other. Degrease the parts. Then apply a smear of Loctite/Permatex on the base of the key and on the inside edges of the carrier trough. Do not apply it to the threads of the screws. Press the key into place and tighten the screws. Then torque them to 55 in. lbs.

The carrier installed, ready for the key screws to be staked.

Wipe the excess Loctite off the exterior and interior of the bolt tunnel. Stake the screws into place. Use a MOACKS, it is the best. You can get by with a small chisel and a hammer, but neither you nor the carrier will like it.

Let the Loctite cure, and you’re done.

Why all this?

The gas key transfers the gas to the carrier interior. If there are leaks, the gas pressure inside the carrier decreases. That means less force to drive the system, and the result is what is known as a “short-stroke” malfunction. This typically happens only after you’ve been shooting for a while, and the gun gets dirty and dry. Lube is important, as we’ll cover later.

The MOACKS not only stakes gas keys, but it cleans many parts on the bolt, carrier and firing pin.

The typical manifestation is in a class, one starting on Monday morning. By Tuesday afternoon, with a lunch break, and tired students who haven’t lubed their rifles, the gun is dry, the key leaks, and when they start shooting after lunch, violá, short-stroking. In the past, the response was “Lube it, and keep shooting.” Today, we know that there can be more involved. It only takes a moment to check, and if the key is loose, a few minutes to correct forever.

HOW LONG DO KEYS LAST?

Keys live longer than gas tubes. The key is hard-chrome lined, and the donut on the tube wears faster than does the key. You could probably go through several barrels and gas tubes before your key is a problem. Well, key wear, anyway. What you have to watch out for is dropping it.

An acquaintance of mine is a long-time US Army NCO, who had lots of experience with the system. He told me that one of his friends had made up a special tool. It was a hardened steel post that was the correct diameter of the interior of the gas key, with a bevel on it matching the interior angle of the key opening. You see, when the various Army teams would travel to compete, the rifles traveled in one truck, while the bolts for them were in a different truck, in the same convoy.

The staking bolts crush metal over onto the key screws, keeping them from loosening and backing out.

So common was it that keys got dinged in transport, that this senior Sergeant made a tool to swage them back into shape.

You can make such a tool if you want. If you have the tools to do it, you also have the knowledge of how to measure and make one. If you do not have the tools, your option is to buy a new key, replace the dinged one and learn your lesson.

LEAKY BOATS

Assuming you have a high-mileage rifle, and in the rebuild you find that the gas tube is worn, what can you do? The end of the gas tube, where it pokes into the upper receiver, has a donut-like ring on the end. This is the tube seal. The opening of the key is a funnel, and the end of the tube is tapered, so they are self-centering. But if the gas tube is a bit off center, it wears on the high spot. If it wears enough, it can leak. But that is a lot less likely, as the interior of the key is hard-chromed. More likely, you dropped the carrier, it landed on the key, and the key is now bent or dinged, and useless.

Time to change the key. Find an Allen wrench that fits. (Unfortunately, the correct cap screw for the key comes in two different Allen wench sizes. Curse the makers while you try the other one.) Use the wrench and a lever if you have to, and loosen the screw. If it is bound tight, one of three things will happen: the screw will come loose, the head will break off the shaft or the Allen socket will get stripped or rounded out. We’ll cover these in order.

Gas keys are replaceable parts. If they wear too much, and start to leak, yank them off and install new ones. Life is too short to put up with misbehaving, inexpensive parts.

If the screw breaks loose, stop. Now do the same to the other. If you try to unscrew the one screw, it will lift up against the staking, tip the key, bind the second screw, and you will get no further. Loosen the second screw and work them out in turn, removing the key. This is why when you were applying Loctite to the key you did not apply any to the threads.

If the head breaks off, stop. (The two actions feel different, you will be able to tell which is which when it happens.) Now loosen the second screw. If it loosens, or breaks, you are riding high. Remove the heads/screws, and toss the old key away. You have no use for it, nor for the old screws. Grab the stub of threaded shaft in the carrier with a pliers and unscrew it. Need I point out, again, this is why you did not apply Loctite to the threads?

If the Allen sockets round out, take your carrier to the nearest bench grinder, and grind the heads off the carrier key screws. Why not do this first? Because it is more work than simply unscrewing properly secured screws, that’s why.

With the old key off, step back to the installation process, and attach the new one using new screws.

NOT ALL CARRIERS NEED THIS

None of the piston system carriers need this. They are either machined integral to the carrier or they are dovetailed and bolted on. There is one, however, that takes a different approach, and that comes from LWRC.

The LWRC DI carrier has the base and shoulder of the key machined as an integral part. To that they attach a wear part spigot onto the shoulder. The spigot can be replaced if it becomes worn or damaged, but the design does not permit gas leakage. The spigot is held in by threads, and then locked in place with a cross-pin.

If you have this, you not only have a key that won’t leak, the carrier is plated and easy to clean.

SPECIALTY CARRIERS

Let’s talk exotic carriers. The sculpted, the aluminum, the titanium and the unobtainium carriers. What’s up with those? Simple: competitive advantage. By taking a regular steel carrier and carving all the “unessential” steel out of it, or making one from aluminum or titanium, the manufacturer has reduced the reciprocating mass.

With less mass banging back and forth, there is less balance disturbance of the rifle as it cycles. (Honest, some shooters can feel this, or say they can.) What really matters is that there is less mass to bottom out and cause a thump at the rear of the recoil cycle.

This does not come without cost, however. The reduced mass of the reciprocating parts means there is less mass to strip a round out of the magazine and shove it up the feed ramp into the chamber. If your rifle is dirty, dry, dusty, carboned-up or otherwise not feeling its best, the decreased mass might make the difference between closing or not.

JP Enterprises makes lightweight carriers meant for competition. However, these should not be used in a duty or defensive rifle.

There is also the matter of less mass to accept the drive cycle of the gas flow. Less mass means higher cyclic velocity, and the parts come back faster and bottom out harder. They also rebound sooner, and with more velocity than the design was really built to handle. This can mean that the bolt comes back to the magazine early, stripping off a round when the magazine isn’t ready. But ready or not, the bolt is coming, and that can mean malfunctions.

If you put a high-tech competition carrier in your rifle and now it suddenly doesn’t work, throttle back the gas. The lighter parts don’t need as much of a boot in the butt. You need to control gas flow to avoid malfunctions. Which is the main reason competition rifles have an adjustable gas block built into the system, right under the handguards.

Not having built one in, your lightweight carrier can give your rifle problems. If it's meant to be a competition rifle, then go for the lighter parts and control gas. If it's intended as a general use or defensive rifle, use the original carrier, you need the weight.

CARRIER LIFE

Being the guy in the know, and with spies in all locations on the planet (or so some readers suppose) I get sent all sorts of interesting information. One of them concerns a recent incident with the US Border Patrol. Apparently, someone from the higher echelons of management, sent armorers around to all the Border Patrol stations with orders to fully inspect all M4A1 carbines in use. In the course of inspecting, they apparently “deadlined” (that is, required removal from service) 65-70 percent of all rifles. This of course came as a surprise, and the powers-that-be had not planned to replace or repair that many rifles. So, the BP agents were reduced to one rifle per agent or less.

Now, in a city department, having one rifle for every other officer is not a problem. Backup is mere minutes away, and taking cover behind something substantial is an accepted practice when outgunned until the cavalry arrives.

However, Border Patrol agents are often miles and miles from anyone who might help. And they are in rifle country, with nothing solid to stay behind until help arrives. Not having rifles is a big problem. And there was a lot of consternation until the shortfall was corrected.

One of the tools the armorers used was a gage I had never heard of called a Gage, Gas Seal Hole, and is meant to be utilized at Depot-level maintenance. It measures the wear in the carrier bore hole, where the bolt tail seals. If the gage goes all the way into the carrier, the carrier is worn out.

That such a tool exists does not surprise me. After all, the government has to have standards, measurements and inspection tools for everything.

Gemtech makes a special suppressor-ready carrier, one that can deal with the increased dwell time. It’s available in both 5.56 and 7.62 sizes. If you shoot suppressed you should get one.

What would surprise me is that any carrier, well, any properly-made carrier, would fail this gage. Look, we have a hardened-steel part with wear surfaces that are hard-chrome plated. Rubbing against it is the tail of the bolt, but it isn’t really rubbing against it. The gas rings and the bolt body keep the bolt pretty well centered in the bore hole. The amount of actual rubbing has to be pretty minimal, and most of what is going on is carbon being created, ground off and pumped out of the gap. If there is gas leakage in that gap, I can see where the problem might be wear on the bolt from over-enthusiastic cleaning. But the carrier? I guess anything is possible.

Considering how grossly over-gassed even a properly gassed AR is, I’d bet that even if you had a carrier that failed this gage, you could assemble it into a rifle and never notice the failure on the part of the carrier. Now, if you want to track down one of these gages and use it, go ahead. But don’t think it is gaining you any advantage over your fellow shooters. And don’t think the gage will be cheap, either.

If this was your original carrier, you’ve certainly gotten your money’s worth out of it if you have worn it out. Let’s just assume, for a ballpark figure, that the carrier in question has survived a decade of constant use. You’ve plugged four replacement barrels into the rifle, each with its own bolt. So, the original barrel and bolt, plus four more, at $75 each for the bolts and $150 each for the barrels. That’s $900 just in parts. Each of those bolt/barrel combos lasted you, what, 10,000 rounds? So that’s 50,000 rounds (don’t forget the original parts) and that, at the current price of ammo of roughly $300 per thousand, ran you $15,000. So, all told you have gotten the price of a new compact car of use out of that carrier. A new carrier to replace it costs you somewhere between $150 and $200.

Go ahead and splurge, buy the replacement one with the super-high-tech plating on it, to make it easier to clean. The extra $25-$50 is nothing in the scheme of things.

BOLTS

Bolts are a wear part, which means no bolt lasts forever. In fact, the bolt is probably the part that has the shortest life in your rifle, as it certainly is subjected to the highest stress. The AR-15 bolt is a small, thin-skinned, hardened part that is subjected to immense pressure and stress.

The mil-spec calls for a steel known as Carpenter 158. You will search in vain in the SAE catalog for it, as it does not have a series number. A series number is something like 4140 or 316. In carbon steel, the 4140 means it is a 41-series alloy, with 0.04 percent carbon.

A properly tested bolt will be marked “MP” and some other letter or number.

Carpenter 158 is made by the Carpenter Steel Company, and it is their 158 alloy, specifications known only to Carpenter and the government. Carpenter gives enough of the details, the ingredient list if you will, so that an educated and experienced engineer can figure out if it is what they need. Carpenter makes it in batches, very carefully controlled and precisely handled, so it is consistent as possible, and within specification.

What this means is, if you want Carpenter 158, you buy a batch. They do not make it as an inventory item, it is made in batches, and if you want it, you buy it. If you and someone else can split a batch, that isn’t Carpenter’s concern, but you cannot place an order for, say, ¹⁄₁₀th of a batch’s weight and have them ship it.

However, to a certain extent, steel is steel. If someone has a full laboratory, and the knowledge of how to inspect, they can take a mil-spec bolt, see what grain structure it has, what hardness the various parts have, and reverse engineer an alloy. And since the TDP, or technical data package of the M16 is owned by the government, they say who gets to read the actual specs for Carpenter 158. If you don’t have a contract that involves M16 bolts, you can’t have the specs. If you do have the specs, you can’t necessarily use them to make outside parts. It’s all in the contract.

That’s the long way of explaining why not everyone makes bolts out of Carpenter 158. Also, Carpenter 158 was developed back in the 1950’s. While I’m certain Carpenter has improved it since (as long as it performs at or above the required specs, and has the recipe mix they told the government it had back in 1964, they can improve it all they want) I’m also certain there are alloys that work as well or better that have been developed since.

It is entirely possible, and they are not blowing smoke, that a bolt maker or AR builder is using a steel better than Carpenter 158.

But, we need to get back to bolts and how they are made.

Bolts are turned on a lathe. The bolt is a cylinder with segmented teeth, the locking lugs. It is relatively easy to use a lathe/mill CNC machine that will first turn the parts as cylinders, then orient them to cut the locking lugs, extractor socket and drill and bore the cam pin hole. The difficult part is in hardening it.

The lugs and the webs between the various components of the bolt can be quite thin. The bolt, in order to have sufficient wear characteristics, and strong enough to take the load, has to be surface-hardened. If the hardness is too thin, the load-bearing parts can peen, or upset. If the hard layer is too thick, the bolt can be brittle and shear off when the load becomes too great. And since the rear surface of the lugs have to be axial and an exact distance from the bolt face to control headspace, there isn’t a lot of wiggle room there.

Once made, the mil-spec calls for several extra steps. First, the parts are shot-peened. This involves what amounts to sandblasting, but with mild steel shot instead of sand. The pellets are streamed at the part, and the impact acts to stress relieve and surface harden the bolt. This can greatly increase the service life of parts so treated. However, it requires an exact knowledge of shot size, velocity, impact/flow rate, and time of duration. Also, the useful life of the shot has to be monitored and controlled.

The end result is a very tough, durable, hard and expensive part. But wait, there’s one more test.

In the mil-spec process, each and every one of the bolts is placed in a fixture, and subjected to the impact of a proof-round discharge. Then, it is given a magnetic particle inspection. This involves subjecting the bolt to a magnetic field and applying a powder that is magnetically sensitive. If there is a crack, or a large stress in the bolt, the magnetic field will be disrupted, and the alignment of the powder will show it.

The specifications are known only to those with the contract, but a certain number of bolts are allowed to fail the proof test in each production batch. And a certain number are allowed to fail the inspection. A part that passes is marked in typical Colt fashion with an “MPI,” with other companies using similar markings, such as “MP.” In the mil-spec process, if more than a certain number of bolts fails, the whole production lot must be scrapped. Not just stuffed into a dumpster, but mangled beyond use.

Manufacturers have lots of parts on hand, and can mix-and-match a bolt to a barrel for correct headspace. If you are replacing a barrel, it would be clever to order a new, headspaced bolt with it.

That is why USGI bolts, complete with MPI markings, cost so much. Each and every one of them was tested and passed. But, in a theme you have no doubt noticed, this is not without cost. It is a statistical certainty that the pressure testing of the bolt, when made, and then again when the rifle is assembled, reduces the service life by a significant amount. Let’s say that the government ceiling on service life of a bolt, 7,500 rounds, is several thousand rounds less than if the bolts had not been so hammered by proof round testing during manufacture. But, the government would rather have a 100 percent certainty that they all pass, even if it means a somewhat reduced service life, than one in a thousand quitting in a much shorter time period, say a few hundred or a thousand rounds.

It isn’t just a matter of statistics, but what you want the statistics to tell you.

So, let’s put a bolt together.

BOLT ASSEMBLY

You’ll need a small hammer, a set of punches, a bolt fixture such as those from Brownells, the bolt and its parts. Give the bolt a good inspection. Now is the time to find cracks and chips. Make sure if you paid for a bolt that went through the magnetic inspection that it is marked as such.

Check that the cam pin you are going to use fits the bolt. If you are using a new bolt, you should be using a new cam pin. They are an inexpensive, hard-used part and, while they do seem to last forever, why not spend the extra $5 that it costs?

Do a quick check of the ejector you’re about to install. The top edge should have a very slight bevel to it. If it is dead square, it will shear brass and eventually bind. If it has too large a bevel, it will shear brass and eventually bind. Just like Goldilocks, you want just enough.

This is a bolt disassembly tool. If you ever plan to take the ejector out of your bolt, you’ll need this.

Put a drop of oil into the ejector shaft. Slide an ejector spring in. Slide the ejector in and make sure its relief cut is oriented toward the retaining pin hole in the bolt. You can look through the hole and see which way the ejector needs to be. Now place the bolt into the fixture. Align the ejector retaining pin hole with the clearance hole in the fixture. You won’t need the clearance hole on assembly, but it is a good habit to practice.

Turn the handle of the fixture, which compresses the ejector down into the bolt. Once the handle stops, look through the retaining pin hole and make sure the ejector clearance is correctly aligned.

The retaining pin will not move the ejector to create clearance. You must compress the ejector so it will clear the retaining pin. Do this as many times as it takes to get it right. If you don’t, you can bend or break the retaining pin when you try to drive it into place.

Once in, unscrew the handle and remove the bolt.

Next up, the extractor.

The extractor will probably come bare, with no spring on it. If you are buying all new, and the extractor is offered with the spring installed, buy it that way. You need the extractor, the extractor pin, internal buffer, extractor spring and an O-ring or D-Fender.

Put the internal buffer inside the spring. The spring will be a tiny little spring cone; you want the fat end of it in the extractor seat. Place the little flange of the internal buffer (or the nail-head if you will) against the extractor. You cannot simply press the extractor down into the seat. The recess milled in the extractor has an underlip, a recess cut in it for the spring diameter. To press the extractor spring down into the extractor, you need a tapered pin punch or the tip of a loaded round.

Keep the spring centered on the extractor recess and press straight down on the top center of the spring, compressing it into the recess. When you hear or feel a slight snap, the spring has been seated. Alternately, you can use the tip of a knife to press down on the bottom coil of the spring only. Slip the knife point into the spring, depressing the last coil into the recess.

If your ejector does this, then you need to track down the sharp edges and slightly bevel.

Slide the O-ring or D-Fender over the extractor spring. Place the extractor in its slot in the bolt and press the extractor in with your thumb. The easiest way to get the extractor pin across is to pinch the bolt at the extractor, compressing the spring and rubber booster.

Start the pin, pressing for all your hand strength is worth, pushing the pin through when the holes line up. Use a small hammer to tap it flush, and you’re done.

Once assembled, apply some oil. A drop in the gap of the extractor, at the point where the pin goes through, is all you need at this time.

An ejector with shaved-off brass particles, keeping it trapped inside the bolt.

POF ROLLER CAM

As uninteresting as the cam pin may appear, it serves a vital function. When the carrier cams the pin on closing, the pin tips off of upright. Look at the squarish lump on the left side of your upper receiver. That is the recess into which the cam pin tips when it cams. When the bolt opens, the cam pin turns back upright, sliding back and forth in the area of the upper receiver where the gas key and charging handle cycle.

CAM PINS

Blueprints have tolerances. If something is supposed to be 1.000 inch in size, it will be listed as 1.000 +/- 0.001, for example. This means it can be as small as 0.999 inches or as large as 1.001 inches.

The application determines the dimensional tolerances. A 1-inch steel rod bought at the hardware store could have a tolerance spec of +/- .010, or 1.010-.990 inches. The same part in an aerospace application could have tolerances as tight as +/- .0001, or 1.0001-.9999.

The blueprints for the cam pin, and the cam pin hole in the bolt, have wide enough tolerances that some will be a press fit and won’t work together. Theoretically, if you made cam pins to the full allowable dimensional spread, ditto bolts, half of them would not fit. The hole in the bolt has to be kept as small as possible, because the bolt's sidewall is quite thin. That means the manufacturers have to take up all the dimensional variance in the cam pin.

And there’s the rub. If they make the cam pin too much smaller, it will tip in the bolt, create extra stress, bind and wear faster.

Something so apparently simple and so prosaic to function like a cam pin is actually an object of much engineering agony, fussing and concern.

Frank DeSomma at POF designed a cam pin with less friction. The simple approach was to change the rectangular head of the pin, replacing it with a roller bearing. The POF cam pin is plated, making it easy to swap. Disassemble the bolt, pull out the cam pin, plug the POF pin in, and reassemble. Job done.

Does it do a lot? Probably not, but an incremental improvement is still an improvement. If you can add in ten changes that each improve the system by 1 or 2 percent, you have improved the system by 10-20 percent. That’s not nothing.

If you are building a rifle from scratch, the extra few dollars for the POF roller cam pin is worth it. If you want to make a competition rifle a bit smoother, get one and install it. The mil-spec-or-nothing crowd will mock you, but as I’ve said before, let your scores do the talking.

HEADSPACE

When it comes to the AR-15, almost nothing exceeds the volume of misinformation as does headspace.

If someone tells you that all you need is a USGI Field gauge, stop talking to that person right now. Stop listening to anything they have to say. Just walk away. Oh, there might be useful information there. After all, you have to paw through a lot of gravel to find a nugget of gold. And telling you that a Field gauge is the only tool you need is definitely gravel.

What is headspace? In simple terms, it is the amount of room in the chamber for the cartridge to rest before it is discharged. The measurement is defined as the distance from the face of the bolt to what is called the “datum line,” which is a particular location on the shoulder of the chamber of a given diameter, and a stated distance from the face of the bolt. The idea is to provide enough room for the loaded round to fit, even when the rifle is dirty, choked with carbon or just not squeaky clean.

Similarly, ammunition is manufactured so the distance from the base of the cartridge to the shoulder will always fit into a chamber. The tolerances of the loaded round and the chamber into which it fits are not allowed to overlap — the largest cartridge made must fit into the smallest chamber made.

Alas, not everything can be made to exact dimensions. So, the chamber is allowed to vary slightly. Generally speaking, the allowable “drift” of the headspace dimension is 0.006, or six-thousandths of an inch. If headspace is within that spread, it is deemed to be correct.

You can see how the bolt locks into the barrel extension. Note that POF makes barrel nuts that act as heat sinks to pull heat away from the chamber.

To measure headspace, there are three kinds of instruments. One is called a “Go/No-Go” gauge. Another is a set of precisely ground and measured gauges, each .001 inch difference in size. And finally, a micrometer that looks like a headspace gauge. Each works differently.

The Go/No-Go gauge is simple. The Go gauge is manufactured to the largest size of a cartridge. If you can close the bolt on a Go gauge, things are good, as the chamber is not below minimum.

The No-Go gauge is made to be a small amount larger than the largest allowable dimension of the chamber. If a bolt closes on a No-Go gauge, the chamber is too big. But, what does that really mean? When you fire a round, the case expands to fill the chamber. If the shoulder of the chamber is forward of the shoulder of the case, the case expands to fill the chamber. The shoulder must then blow forward to fill the gap. The rear goes back to the bolt face. In the middle, brass gets stretched.

Now, in the microsecond in which this happens, it can proceed in several different ways, but the end result is the same: the case gets stretched in the middle, weakening it. This matters only to reloaders.

Re-sizing brass pushes the shoulder back to minimum (this is called the “shoulder bump” and it ensures your loaded ammo will fit your rifles) and the next time you shoot, the brass will be stretched again. The effective service life of your brass depends on how much stretching, and how much bumping you subject it to. If your headspace is within accepted limits, you can get 10 or more loadings out of your brass before you start seeing neck cracks from work-hardening. If the headspace is excessive, you may only get two or three.

An exemple of this is the SMLE in .303 British. The .303 headspaces on the rim, not the case shoulder. The British Army cared not a whit about reloadability, only for reliability. I gave up reloading ammo for my various SMLEs because I could not get cases to last more than three loadings in any of them.

The US Army, Marines, Air Force, and let’s not forget the Coasties, do not care about reloadability of brass. As long as the brass holds together and is ejected in a single piece, they are happy. And that is where the Field gauge comes into play. The Field gauge has been developed with one thing in mind — how large can the chamber be and still have a rifle that can be used in a wartime situation? And that is why military armorers have a Field gauge that they use commonly, rarely reaching for their Go and No-Go gauges. An armorer may have a rack filled with rifles and carbines that would easily gobble up a No-Go gauge.

Use of the Field gauge only applied to used rifles and carbines. If a brand new, fresh out of the box unfired rifle is tested, and the bolt partially closes or locks on a Field gauge, it should be sent back, even in military use.

Why then is a Field gauge not a good choice for you? In short, you aren’t going to war. You will likely be using reloaded ammo. You have an interest in making that brass last as long as possible. If you need headspace gauges, get a Go/No-Go set.

What of the others? The “thousandths” set is used to determine not just that the headspace is within tolerance, but precisely what it measures. The micrometer gauge does the same thing, but instead of having to check the fit of the gauge set, you install/assemble the micrometer set, adjust, and then read the measurement.

The cognoscenti argue over the commercial .223 versus the mil-spec 5.56 headspace gauges. I talked to Dave Manson, a maker of headspace gauges about this. His quick reply was, “Which 5.56 set?” It seems there are a whole raft of gauges and specifications out there. And that is just in the shoulder location, not including the leade, which we’ll get into in a short bit.

How much can these vary? Let’s look at a few dimensions, hunted down and laid out for your curious gaze.

View a text version of this table

So, if you have a rifle chamber just over the max size, call it 1.470 inches, and your sizing die is set to bump the shoulder back to fit under the minimum chamber size, let’s call that 1.460 inches, you are working your brass .010 inches on each shot. It isn’t going to last long.

MEASURING

To measure headspace you’ll need a chamber brush, cleaning rod, bolt disassembly tool and a set of headspace gauges.

Unload your rifle and separate the upper from the lower. Use the chamber brush to scrub the chamber. Clean the bore with a patch to extricate any crud you scoured out of the chamber.

Remove the extractor from the bolt. Use the bolt fixture to remove the ejector. Scrub the bolt and dry it. At this point, don’t be tempted to just drop the gauge in, close the bolt and see what happens. The closing bolt has enough mass and leverage to close the bolt on even a No-Go gauge if you are forceful enough or let it crash forward under full spring force.

That is the wrong way to be doing it. The right way is as follows.

If you have the barrel out of the receiver, life is easy. Drop the Go gauge into the chamber. Hold the bolt by the tail, and see if you can insert it into the barrel extension, rotating it in front of the locking lugs. You should be able to do this. If not, that particular bolt/barrel combo is out of tolerance, under-minimum headspace and should not be used. Which is at fault? There is no way of telling with the tools at hand. To find out, you need at a bare minimum a surface plate, standing calipers and a bolt face cylinder. The cylinder is simply smaller in diameter than the bolt face opening, and a known thickness.

Put the cylinder on the surface plate. Stand the bolt on the cylinder, and measure the distance from the surface plate (which is flat to a millionth of an inch, if you bought the good one) and then consult the bolt drawing to see what that measurement should be. Without a bolt drawing there’s no real way to know.

If the bolt and chamber accepted the Go gauge, then remove the bolt and gauge, and replace the Go with the No-Go. Try again. The bolt should not, must not, rotate to the closed position. If it does, you have excessive headspace, and as before, you don’t really know which of the two is at fault.

A quick answer, in both instances is, both of them.

What if you have the barrel already installed in an upper receiver? Go to the store and buy yourself a foot of PVC tubing. You want a piece that has a quarter-inch inside diameter, or ID. The outside diameter, or OD doesn’t really matter since you can’t buy it with walls thick enough to not fit into the upper receiver.

Stuff the tail of the bolt into the PVC tube and use the tube as a handle to hold the bolt, as you insert it into the chamber while doing the Go/No-Go test.

If you have a case separation, you’ll know when the rifle won’t close, and when you do get the bolt back, this comes out.

CORRECTING WRONG HEADSPACE

The first thing to do, if you have the gear and parts, is check the headspace on a rifle that has worked. If you are building a rifle from parts and do not have a working rifle to check, then you need to borrow one. Or go to the gun club with your parts and tools, and ask someone if you can measure theirs.

If the other rifle checks out, then send the parts back. If the other rifle doesn’t pass muster, then check your technique. The odds of two rifles from different sources both having incorrect headspace is exceedingly low.

Back in the early days, we ran into incorrect headspace frequently, as many people who were making parts were either new or not very good at it. I also suspect that a lot of the bad parts we found at sale prices in gun shows back then were production rejects, out of spec and should never have been sold. The bad parts makers got their names bandied about enough that they either improved or quit. Now, everyone who is still in the business knows the proper bolt or barrel extension dimensions. However, you may still find some parts that do not agree.

Brand new parts should fit. If you got the bolt and barrel from the same source, contact them and arrange an exchange. They should be happy to do so. If you got them from two sources, contact each and explain the situation. See which, if either of them, will help you. Accept their help and strike the other company from your list of “doing business with” for the future.

Only in extreme circumstances should you even think about chamber reaming to adjust headspace. And then only if the barrel is stainless or un-plated carbon steel and un-returnable. You can only correct insufficient headspace by reaming. If you have excess headspace, and you cannot return the barrel, then your only other option is a session with spare bolts and your headspace gauges. Maybe you’ll find a bolt that would otherwise be too big, but will solve your excess headspace problem.

REAMING HEADSPACE

I have reamed chambers and adjusted headspace in rifles without removing the barrel from the receiver, so it can be done. Having done it, I have to tell you this: remove the barrel. The hassle of reaming the chamber with the barrel in the receiver is greater than the hassle of removing the barrel and then reaming. Plus, you can do a better job with the barrel out. So, you’ll need the barrel and bolt, the finish reamer for 5.56 (not .223 Remington) with handle, cutting lube, chamber brush and a cleaning rod and patches for the bore once you are done.

Clamp the barrel, padded, upright in your bench vise. Scrub the chamber. Strip the bolt and scrub it clean. Check the headspace, just to remind yourself what under-minimum headspace feels like. (The bolt won’t rotate closed with the Go gauge in the chamber.)

Insert the reamer in your tap handle or reamer holder. Gently lower the reamer into the chamber, and begin rotating before it contacts the shoulder. Only turn in the direction of cutting, never reverse rotation. Give the reamer two full turns once you feel contact, pull it out while still rotating, and inspect the reamer. You should see metal chips on the shoulder of the reamer. If you also see chips on the body, you’re getting a bonus in the headspace adjustment; you’ve got a narrow chamber and the reamer is correcting that. You won’t have to mess around with small-base dies when you go to learn reloading.

Swab out the chamber and recheck headspace. With a few iterations you will get to the point where you can feel the bolt lugs start to cam underneath the lugs of the barrel extension. Repeat the two-turn cutting procedure until the bolt will just rotate closed on the Go gauge. You have minimum headspace at this point.

You now have a decision to make. You can leave it at minimum, reassemble the barrel into a rifle again, and test fire it. You’ll probably find that it is plenty reliable, and unless you insist on shooting it in miserable environmental conditions it will serve you well.

If you want it to be a little more forgiving of neglect, you have to increase headspace past minimum, but not too much. Remember, the .006 inches of gap is all you have to work with. Measure the overall length of your Go gauge. This is not the headspace, just the length of the gauge. Now carefully apply a small piece of tape to the base of the gauge and measure again. You have just added a few thousandths to the Go headspace, by the thickness of the tape. Do the two-turn ream again, install the taped gauge and measure.

You can, if you are careful and diligent, add a controlled number of thousandths (adding .002, .003, or .004) to the minimum headspace, and not exceed the maximum.

Once you are done, scrub the chamber. Push a clean, dry patch down the bore to get lube and metal chips out of the bore, reassemble the rifle, and go to the range to test-fire and re-zero.

Remember, you can adjust headspace only when the chamber is under minimum, and the barrel material is stainless steel or un-plated carbon steel. You cannot adjust the headspace on a chrome-lined barrel, or one that has been treated via the Melonite process.

Why a 5.56 reamer, and not a .223? Because you want the leade to be 5.56. If your chamber is not only under minimum, but has a .223 leade, then the headspace reaming operation will take care of both.

EXCESSIVE HEADSPACE

If you have too much headspace, and your brass stretches, then what? Basically, subjecting the same brass to excessive headspace too many times will cause it to break in the middle. You probably won’t know it, because the broken rear half will be extracted and ejected. But the next round will find the front half crammed in the chamber. The fresh round will wedge hard into the remaining piece, locking the rifle up. You’ll have a heck of a time clearing the jam.

If you are using commercially reloaded ammo, it is possible for the brass to have been abused before it got to you. If it had been fired in something with grotesquely excessive headspace, like an M249 SAW, then it would have been stretched at that time.

So, a singular event, in reloaded ammo, may not be your rifle’s fault.

But check anyway.

BOLT WEAR AND SERVICE

If you shoot your rifle, you consume parts. With the possible exception of the carrier (the jury is still out on that one, given the new information) everything on your rifle has a service life. Bores and leades wear, bolts eventually wear or crack, and even the buffer spring has a cycle life. It may be a million cycles, but it has a life. So, what do you look for on bolts and parts?

First up, the gas rings. By far the shortest-lived part on the bolt, gas rings can last thousands of rounds or quit in hundreds. It depends on the interior of the carrier bore’s smoothness or lack thereof. The classic test is to take a clean and lubed bolt/carrier assembly out of the rifle. Extend the bolt so it is fully forward of the carrier, and then stand it on its head. That is, stand it on the bolt face.

If the weight of the carrier causes the assembly to collapse, the rings are worn and you can change them if you wish. Will they still work as-is? Sure. A secondary test is to push the bolt back into the carrier and hold it with the bolt facing down. If the weight of the bolt alone causes it to extend forward, then the rings are worn and you must replace them.

A perennial question is, how many rings do you need in your bolt? As my brother has said, on more than one occasion, “There you go, confusing wants with needs again.” You want three. How many your rifle will work reliably with is what you are really asking, and to that I have no ready answer. There is no definitive answer because every rifle is the master of its own fate. I have one rifle that will pout if it doesn’t run three rings. Needless to say, it isn’t my first choice of rifle for bad times or self-defense. I have another that will function reliably with no rings at all, if you accept not locking open when empty as part of “reliable.”

Gas rings are cheap. Do the test. If the bolt fails the test, replace all three.

Small parts are prone to breakage or loss. Have a spare firing pin, cotter pin and other small parts, just in case.

Second, ejectors. The ejector and its spring, unless you damage them or allow the bolt and spring to become rusty, do not wear for the life of the bolt. The government assertion that the service life of a bolt is 7,500 rounds means the ejector spring has been cycled 7,500 times. It is a poor spring that can’t take 7,500 cycles. If you were really cheap, you could probably get an ejector and its spring to last through five or 10 bolts, but why? The replacement bolt probably comes sporting an ejector, extractor and the springs. Use them.

One easy test is to keep a new ejector spring on hand as a sample. When you pull the old one out (for whatever reason) compare it to the new one. If the old one is visibly shorter than the new, install the sample until you can order a replacement. If it isn’t visibly shorter, put the old one back, it still has life left in it.

Third, extractors. We used to worry and fuss over extractors, but they are pretty simple things. On the front end, all you need to be sure of is that the ledge is clean and has not been machined with a rounded lip, and that the corners have a sharp feel to them. My buddy Ned Christiansen describes the feel as “kitten teeth.”

What really matters for extractors is on the back end. You must have, at the very least, an extractor spring with a little black synthetic buffer in it and a SpecOps/Crane O-ring. Better yet would be an extra-power spring, with black insert and a D-Fender extractor buffer.

From its onset, the Stoner system has been under-extractored. From the original spring-and-no-insert, the government has gone through a spectrum of colors, each darker color having a higher elastomer rating (stronger springiness) until they have gotten to the black ones.

It is possible to have too much extractor strength, but it isn’t likely. You can tell if you are close (and do this at the range, please, with the safety on, and the muzzle in a safe direction). Drop a round in the chamber, ease the bolt forward, not letting it crash into battery. Gently rest the bolt against the case before you let go of the charging handle. The buffer spring should have enough force to cam the extractor over the case rim and close the bolt. If it doesn’t, you are getting close to excessive extractor strength. What is truly too much is, if the extractor can’t cam over the rim in normal cycling.

BOLT INSPECTION

Bolts last longer than gas rings, but they can still wear and break. The most common location is where the two lugs on either side of the extractor crack at the base, sometimes breaking off. Why there? The bolt is designed as an eight-lug bolt, with the lugs evenly spaced. However, to fit the extractor in there, Eugene Stoner had to remove one of the lugs. This left seven spaced as if there were eight. As a result, when you fire, the bolt is unsupported in that area, the stresses acting to tip the bolt. Since the bolt can’t tip, the two lugs outside of the extractor bear a greater amount of the generated stress.

This was one of the weirdest malfunctions we’ve ever seen. The under-powered extractor and the getting-bound-by-brass ejector combined to barely eject this empty. It then got caught by the carrier and clamped in place.

STEEL AND EXTRACTORS

Do steel cases cause extra stress and wear on extractors? That’s an experiment I’ve been looking to conduct for some time now, but have not yet worked out a methodology that satisfies my scientific requirements. However, I did conduct an inadvertent experiment. I'd chrono’d a bunch of different loads, and used a power saw to trim the barrel back 1 inch for each velocity measurement.

This precluded a self-loading rifle, since there was no way to have a gas port that worked with all those lengths. (Especially the ones shorter than the gas port location.)

I had to hand-cycle the rifle on each shot. What I discovered was that yes, some steel-cased ammo extracted harder (and I tested over 2,000 rounds in total, I got good at hand-cycling an AR-15) but not all. And some brass-cased ammo extracted as hard or harder than the steel-cased. Yet, some of the steel-cased ammo was relatively easy to extract.

So, the answer is: Yes and no.

If it really worries you, buy an extra extractor, spray-paint it a bright color, and install it for use while practicing with steel-cased ammo only. Save the original for brass or match use.

In normal use this doesn’t matter, at least not in a statistically significant way. Low-quality bolts, badly made barrel extensions and excessively powerful ammo can increase the rate, but we’re still talking about something a lot less than 1 percent of the time.

What does cause problems are SBRs. And especially SBRs with suppressors. The greater gas volume, and higher peak that many SBRs generate, cause the bolt to be unlocking while the case has not yet relaxed from expansion. The increased dwell time of suppressors only adds to that stress.

When bolts break lugs they usually shear on either side of the extractor.

Christiansen has had occasion to do armorers work for some very special organizations. One in particular runs a fleet of several hundred suppressed SBRs. Every time he shows up, there is another shoebox of broken bolts for him. He dutifully inspects the rifles and usually finds a few more — rifles that were still functioning even though the bolts were cracked.

You can inspect your own bolt with it still in the carrier, but it is easier if you remove it. Here’s the process. Thoroughly scrub and then degrease the bolt so it is bone dry. (Needless to say, re-lube before assembly, once you are done.) Look closely at the base of the locking lugs on either side of the extractor. The cracks usually proceed on a diagonal line from the root of the lug. No cracks? No problem, especially if you are not SBR’d or suppressed. If you are, make this inspection a regular part of your cleaning and maintenance.

If you find such cracks, replace the bolt, check the headspace with the new one and keep shooting.

A few years ago, we were seeing a mysterious crack at the cam pin hole and failure in bolts. I first noticed this in a law enforcement (LE) class, where the students were merrily hosing the targets out to 300 meters. I was in the range tower. “Lane 3, your shot was 10 feet low, left.” Next iteration, “Lane 3, your miss was 5 feet high and right. Off the line and get the rifle inspected.” When we pulled the carrier assembly out of the upper, the bolt fell out onto the ground.

If your bolt breaks like this, it is probably a high-mileage part you should have swapped out sooner. If not, you may have the rare rifle that is grossly over-gassed.

This is a rare breakage that we saw for a few years. There’s no preventing it, just replacing it.

The sidewall of the bolt is very thin at the cam pin hole. As near as we could tell, some sub-contractor who was making bolts for several AR makers had gotten a batch with some problems. Perhaps the case-hardening was too thick, and the sidewall was brittle. Perhaps the deburring wasn’t done right, and the edge was too sharp, causing a stress riser. We don’t know, except that we saw them for a while and then the problem went away. Maybe we used all the bad bolts up.

When you are inspecting the bone-dry bolt for cracks at the locking lugs, take a look at the cam pin hole. If there is a crack, it will be obvious. If you don’t catch it, eventually the bolt will crack through on both sides and the front half will come loose.

BOLT CLEANING

To clean the bolt, scrub the gunk from the front and the carbon from the rear. It does not need the attention a Sergeant will give it in a white glove inspection. But you should knock off the larger chunks of carbon now and then. The best tool for this is one of the special purpose tools from Avid, Sampson, Otis, M4Cat and many others. Do not use a pen-knife; you will end up cutting your thumb. Do not use a cleaning brush, as you risk hooking one of the gas rings, flinging it into the weeds or shag carpeting.

It need not be squeaky clean. Simply make sure there isn’t a big hard ring of carbon hanging on.

Lube the ejector, extractor and rotation bearing ring on the bolt body. A drop of oil rubbed around the rear side of the lugs will suffice, and back into the carrier it goes. You’ll apply more lube later, so don’t get too worried about oiling everything now.

BETTER BOLTS

It has become common for inventors, manufacturers and gunsmiths to offer new and improved bolts. Are they really that much better? The quick answer is yes, but it depends. As I’ve said before, and some of you are already mentally forming the words, the AR-15 is the epitome of 1950s technology. The alloys, surface treatments, quality standards and expectations are all from the Eisenhower Administration. It would be a staggering miracle if it wasn’t possible to make a better bolt, barrel, whatever. However, knowing and proving are two different things.

Just because someone says they use a better alloy doesn’t mean they have proved it. And a better alloy may make a better bolt, but by how much? To know that, you have to test to the point of destruction a statistically significant number of any given product.

Manufacturers have to make bolts within very strict tolerances. But they still have small variances in dimension and that’s where headspace tolerances come in.

However, if someone is offering a “better bolt” and the product isn’t at least as good as the original, they won’t be in business for very long. It follows then that if someone has been making and selling an improved bolt for a few years, it probably is better.

There’s also the matter of the AR as a system being a known quantity. You can take a reliable, accurate AR, and swap the bolt (check the headspace, of course) and if it remains reliable in function and accurate, you can be pretty sure that the new bolt is working as it should. Will it outlast an original one? You’ll have to wear out a couple of barrels to find that out.

SHARPS RIFLES BOLT

The Sharps is one of the improved bolts using better steel alloy and modern stress analysis to make it stronger. To make something stronger, you either make it larger or you improve the alloy, or both. In the AR, you are limited in size. The bolt has to fit the carrier and barrel extension, and that is that. But you can change the shape of the locking lugs so as to reduce the stress riser effect.

Stress risers are details of design, or manufacturing, that act to focus stress to a small area. One example would be a sharp, ninety-degree corner on a strength part. The sharp corner acts to focus the stress the part undergoes, and it will break early. If instead the corner is machined with a radius, the smooth curve does not allow the formation of a stress riser.

Similarly, a heinous tool mark can act as a stress riser, which is why bolts are shot-peened. Peening reduces the size of tool marks, which are unavoidable.

The shape of a part can focus stress. By removing metal in a controlled way, from a certain area, you can redirect stresses so they can’t become focused or concentrated.

As an aside, Sharps is not the only company to do this. LMT also has spent a great deal of engineering attention to bolt lug design to reduce the stress focus effect.

The Sharps bolt is made of S7 tool steel, which is a more modern alloy than Carpenter 158, with advantages in some aspects.

Assuming the barrel is headspaced within tolerance, the Sharps drops in as a straightforward replacement for your bolt. Or, if you are building from the ground up, use a Sharps bolt in a barrel made of stainless steel, reaming the headspace to adjust as needed.

ALEXANDER ARMS

Bill Alexander offers two bolts — a standard and hard-use. The hard-use bolt is improved with subtle engineering changes to the lugs and given an ionbond surface treatment. The end result is a bolt that looks like a regular bolt, but has a much longer service life.

LMT

Lewis Machine & Tool has taken a new approach to bolts. First of all, they did extensive CAD/CAM and solid modeling stress testing, and found that if they removed metal from the lugs, they could make them stronger. They use a newer alloy, which is stronger than USGI. The extractor is improved both on the claw, which grips more of the cartridge rim, but also the extractor spring has been changed. There, they widened the end of it to a lobster tail shape, and packed two springs side-by-side in the bolt to increase extractor tension.

And they modified the carrier as well. There are five vent holes instead of three, and the cam pin track has been changed, to provide a longer dwell time before rotation.

Finally, the bolt is plated with a proprietary coating that increases lubricity, eases cleaning and resists chipping.

This does not come for free. An LMT bolt runs you on the order of $180, (ca. 2016) where a regular bolt might run you as little as $50.

RETRO BUILDS

During the early years of the AR-15, the bolt and carrier of the rifle were chrome-plated to make cleaning easier. The government decided that shiny chrome was not desired in a combat situation, and that the chrome-plating process was too prone to hydrogen embrittlement. They dropped the requirement.

This means that if you are going to build a period-correct AR-15, M16A1 clone, XM-177 or other, you have to find a bright carrier. That means a chrome-plate job, a modern plating that is shiny (although not as correct as a chromed one) or one made of stainless.

That used to be a lot harder, but the progress in AR materials today means finding an acceptable carrier is now as easy as opening a Brownells catalog.

One thing to keep in mind is that some very early models did not have a forward assist, and finding a period-correct carrier without the notches isn’t easy. However, the government never really cared about details like that, so it would not be unusual to find a rifle or carbine lacking a forward assist that had a notched carrier. The Air Force in particular has been in the habit of rebuilding old rifles, and not just scrapping and replacing them.

So look, and build correct, but don’t get too OCD about it, because even a minor difference can be current-issue correct.

DOES IT MATTER?

Does an expensive, high tech bolt make a difference? On the one hand, the government feels the service life of a USGI bolt is 7,500 rounds. And yet, except in the case of SBRs, and especially suppressed SBRs, I have not seen that short a service life in bolts. I have one that is on its third barrel. I know of others, high-volume trainers and competition shooters, who do not see bolts breaking (if at all) in anywhere near that timeframe.

If you want to build a rifle or carbine with a super unbreakable bolt, go for it.

However, if you are building an SBR or a suppressed SBR, I’d suggest that you get the best bolt you can. A suppressed carbine might benefit from upgraded parts, but the real shorties, and those with cans, are definite candidates for a better bolt.

CHAPTER 6
OPTICAL SIGHTS

When the AR-15 was first fielded, the idea of optical sights as general-issue equipment for a military rifle was laughable. No, literally, if you had suggested it you would have been laughed at. Magnifying optics were only just being considered a rational hunting choice in the mid 1950s. They had been around for a couple of decades at that point, but they were still viewed with suspicion by many. They were considered fragile, expensive, prone to fogging and not very durable. Issue high-priced, ultra-delicate optics to troops? That’s just crazy talk.

A personal problem I have is hats. The brim of my hat, and the rear of the scope, sometimes argue over who owns that space. It’s a problem I can deal with.

And then there was that awful carrying handle. Carrying a rifle like luggage? What were they thinking? Not that there weren’t attempts. In the Vietnam War, Colt made (or had made for them by an optics company) scopes that clamped into the carry handle. The problem then, and now, is that while the iron sights are comfortably above the stock, the scope is too high. You don’t have a cheek weld, you have a jaw weld. Cheek weld is the contact surface your face makes on the stock when you are aiming. If the stock, sights and your face are all in agreement, aiming is comfortable — you can aim quickly and well.

If they don’t agree, you have problems.

Back in the late 1970s and early 1980s, Colt offered this clamp-on 3X scope. As a historical curiosity it is great. As an actual tool for improving your shooting, just marginal.

One of the few options we had back in the day for mounting a scope on an AR. It has long since become obsolete.

In the early days, we solved this issue with a quick, easy change — we cut the carry handle off. This was not without its problems. The top deck of the upper receiver, underneath the carry handle, isn’t all that thick. So drilling and tapping a scope base there was problematic. We used several approaches to take care of this. One was to use a gooey, gel-mix of epoxy, sometimes mixed with powdered aluminum, slathered on top of the chopped receiver to fill the gap and hold the scope base and receiver together. Other approaches included milling the front and rear base of the handle so they rode over the scope base and locked it in place. (This took a bunch of hand fitting, by the way, to make it solid and stay in place.)

When the A2 came out, even the hardiest among us couldn’t bring ourselves to chop on it, so we simply chopped more A1 uppers to make scope-equipped AR-15s.

Leupold makes a tough scope mount that is not QD, but has nuts that can be tightened or loosened with either a hex wrench or a flat-blade screwdriver.

When Colt came out with the flat-top receiver, they had a bit of a hiccup. They designed a replacement handle, one that held the rear sight. This handle clamped onto the rail on top, what is incorrectly called a Picatinny rail. Picatinny Arsenal simply looked at it, and said, “OK, do that,” and that was it. Actually, it is properly called a Mil-Std 1913 rail.

The “Pic rail” is a modified weaver base. The modifications include a regular array of cross-slots, to let you lock whatever you desire down in any of the locations available. And the slots are milled rectangular, so their shoulders can be used as recoil-resistant stop surfaces.

Well, Colt designed the top rail and put the dimensions down on blueprints. Then, in testing, they found that the top of the receiver just wasn’t thick enough, lacking the handle as a structural element. So they lifted the dimensional top surface of the Pic rail, making the top of the receiver thicker. Unfortunately, someone forgot to tell the team working on the handle. The handle, and the rear sight, were now too high. The forging dies for the handle and the receiver had already been designed, and would be expensive to alter or replace. In response, Colt raised the front sight post, which is how we got the “F” marked front sights. That said, it is still possible to mount a red-dot scope on a fixed-rail AR, and not have your face a foot above the bore. We’ll cover that briefly, then get on with the flat-tops.

CARRY HANDLE OPTICS OPTIONS

You can track down an old Colt, or Colt-marked 3X or 4X carry handle. These clamp in by means of the hole drilled down through the trough. They are perfect for a retro build, but not much else. The scope (modern copies aren’t much better) had a narrow field of view, poor optical clarity and still sat high above the stock. It also had poor eye relief, and was positioned too far forward.

You can clamp a special handle-fit rail and install a scope on it with a set of rings. This works, but is even higher off the stock than the Colt scope. I built and shot a rifle just like this for many years, but I put a special cheek piece on the stock to give my face a place to rest. Colt made one and sold it to go with their HBar.

Or, you can use a cantilever mount. This clamps in the carry handle, but extends forward over the handguards. Some have adjustments with which to move the scope up or down to locate it just right. Others will be a simple offset. Use regular scope rings to hold the scope on the forward part of the mount and, if adjustable, move it up or down until it has a clear field of view and your face is comfortably down on the stock. This is an adjust-and-try process, there’s no hard and fast rule on placement.

The extension approach has a few problems, not that that kept the government from buying truckloads of them. For one, you can pretty much only do this with a red-dot sight. A magnifying optic that far from your face has to be an extended eye relief, or scout scope. These can be tough for some shooters to get used to. Plus, that can be a lot of weight hanging out on the end of an aluminum bar. Vibration can be severe, and prone to zero shift from getting banged around.

Does this work? Yes. Are there better methods? You bet.

SCOPES ON FLAT-TOPS

Types of scopes for flat-tops include magnifying — divided into traditional and scout style — and red-dot scopes, which do not magnify, but simply create a red dot or pattern that you use for aiming.

Traditional scopes are meant to be mounted a few inches from your eye, and you look through the scope, not through and around it. One could write a book on the details of scopes so I’ll keep it short and simple. Most people mount scopes with more magnification than the rifle can deliver in range or accuracy, or that they themselves can possibly use. The AR-15 is chambered in .223/5.56, which means anything over 9x magnification is pretty much a waste of optical expense, in my opinion. Oh, if you want to punch tiny groups at the range from the bench, then a 4-14x or even more will help you do that.

The Weaver mount uses locking thumbnuts. Tighten the outside levers, then the center locking nuts.

But if you are going to be using it for the kinds of endeavors in which the AR really shines — 3-Gun competition, hunting, varmint shooting — nothing above 9x is going to help. And then there is the matter of cost.

A cheap 4-14x, or an expensive 1.5-5x scope, will cost pretty much the same. You will have a longer service life, and probably a more enjoyable experience with the expensive 1.5-5x than you will the cheap 4-14x.

The scope will not fit well with a fixed rear iron sight. Depending on the particular scope involved, either swap out your fixed for a folding rear, or leave the rear iron sight off entirely. In part, this depends on what application you expect for your AR. Those using it in a defensive or law enforcement situation will commonly opt for a folding rear sight, and a scope mount that is in some way quick-detach in design. A varmint shooter might not have iron sights on his or her AR at all. And some scopes will have such a large rear bell that no iron sight, no matter how flat it folds, will fit underneath.

A good mount positions the scope the same height above the top deck as the line of sight with irons.

There is also the matter of the front sight. The scope mount, if properly designed and installed, will align the axis of the scope with the sights. That is, you will see the front sight through your scope, assuming the front sight is of the fixed design. Some shooters are bothered by this. Me, I never had any problems, and only on a few rifles did I bother to chop off the front sight “A” pillar. That’s right, for a while, in the very early days of 3-Gun and bowling pin competition, I was shooting an AR-15 that had the carry handle and front sight “A” post chopped off. It looked strange until you saw my scores, and then it looked a whole lot prettier.

Today, I’d just build on a flat-top and whatever barrel I used I’d install a low-profile gas block and be done with it.

ONE RING TO HOLD THEM ALL

At its most basic, a Picatinny rail (and yes, it is the wrong term, but it is what people will recognize. Even I get tired of tilting at windmills) is a Weaver rail with a lot more slots. But in a pinch could you use Weaver rings? The problem in determining that is, which ones? The scope has to sit on the centerline of the iron sight axis. That means you have to place the tube center of the scope around 1.40 to 1.45 inches above the top deck of the flat-top receiver.

This requires a bit of arithmetic. Scopes commonly come in 1-inch tubes. If you have 30mm or 34mm tubes, you’ll have to do both arithmetic and conversions.

Weaver ring (and others of the traditional hunting set) height is measured by distance from the bottom of the tube to the top of the base. This means you have to divide the scope diameter in half (thus .500 inches) and then subtract it from the height you need. That gives us a scope ring height of .900 to .950 inches for basic rings. A quick check of the Brownells catalog shows that the tallest Weaver top mount rings max out at .560 inches. That’s not tall enough.

This was one of the problems we ran into when chopping off carry handles and bolting on Weaver bases and rings. You had to use a thick Weaver base, or the tallest rings wouldn’t be high enough to achieve proper aim. But a thicker base added weight, and leverage to break off your mounting system, which usually involves four to six 6-48 screws, each with a couple of threads of engagement and some epoxy holding them in place.

The only other option was to use a set of see-through rings. Weaver see throughs are listed as being .734 inches tall, which brings the scope up to a useful height. But the rings are not exactly sturdy, and they just don’t look quite right mounted on an AR-15. That didn’t keep us from using them back in the prehistoric 3-Gun days, and many a match and lots of loot were won with such a setup.

Still, it is old hat, obsolete, and not really very good-looking. And we all know things have to look good, right?

The solution is AR-specific scope mounting systems.

These come as a complete set of parts. The base, which attaches to the receiver rail, the rings, which are made tall enough to be in the proper location in space, and ring tops or halves. The pillars, the section between the rail and the ring, can be a separate part permanently secured to the base, or an integral part machined with it.

Alamo Four Star makes a riser for your red dot sight which you can hand tighten.

There is another division in scope mounts as well — quick detach (QD) or non-QD. Scope mounts like those from LaRue or American Defense have levers used for attaching or removing the scope. If you have properly adjusted the clamps on your rifle you can pry the scope off in a reasonably quick time. If you need to be able to remove your scope in a few seconds, and have a pretty good return-to-zero (probably a smaller shift than the average groups you’re shooting at 100 yards) then a QD system is great. The non-QD systems, like Geissele, require a wrench to loosen the fastening nuts.

Quality mounts will hold — and return to — zero. Which you use depends on your needs and desires.

For long-range shooting with .308 rifles, a scope mount is defined as either “level” or “zero pitch” or it has a certain amount of down-pitch. The down-pitch is measured in mils, and a 20-mil down-pitch (referred to as a “20-mil mount”) has that angle built in. Why? Because long-range shooters need all the clicks they can get.

A magnifying scope has only a certain number of click adjustments in its up and down range. Let’s use 100 clicks of adjustment as an example. If you start with the rifle zeroed at 100 yards, you most likely have 50 clicks up and 50 clicks down. For a long-range shooter, those 50 clicks above the center of the scope axis are all wasted.

By “up” and “down” we mean the direction the shooter wants to send the bullet’s impact. If you need to shoot out to 300 yards, the bullet will strike low out at 300 with your 100 yard zero. You have to come up a certain number of clicks to strike center at 300 while aiming center. Once you have used the 50 clicks available in the scope, you’re done and can no longer dial-in clicks for longer ranges, even if you have a rifle that can reach farther.

Not all scopes have internal adjustments. The Spectre, from Elcan, features adjustments in the mount, which is a lot more durable.

Assume a click is a mil (it actually isn’t, but I’m trying to keep it simple here). If you use a mount that has 20 mils of down pitch, it is the same as adding 20 clicks of up adjustment. In effect, you now have a rifle with 30 clicks down and 70 clicks up.

For ARs chambered in .223/5.56, a mount with pitch isn’t needed. Even if you are shooting to 600 yards (generally beyond the range at which the .223/5.56 can deliver effective energy) a good scope has enough adjustment without pitch. The optical snobs will maintain that by using a mount with pitch, you are keeping the reticle and your vision in or nearer the optical center of the scope, which is a good thing. But for .223/5.56 shooters, it is more than they need. Now, the .308 shooters can make use of it, but most of the rifles sold of the AR type are .223/5.56 these days.

INSTALLING AND FITTING SCOPE AND MOUNT

First take the top rings off of the scope mount and set them on the bench, arrayed so they are the same way they came off the mount. Don't switch rings or turn them around.

Put the rifle (unloaded) into your working cradle or take the upper and clamp it into a padded vise. Check the fit of the base on the rail and note how far back you can position it without interfering with the rear BUIS. It is not unusual for the sight maker and the scope mount manufacturer to disagree on just how much extra space each needs. You may find that you have to leave a gap between them, as the scope mount stops in a slot on the rail forward of where the sight sits. If you try to move the scope mount back, it hits the iron sight before the next slot becomes clear.

If you have a QD, or a bolt-tight mount, close the QD lever or hand tighten the bolts enough to hold the mount base on the rail. Check that the bolts or the throw levers don’t interfere with anything else on the rifle. A big nut that is too large to pass over the forward assist housing is plenty strong, but if you can’t tighten it, it isn’t much use. A throw lever that can’t close because it is too long (or too far back) to clear the charging handle isn’t much use, either.

Lay the scope in the rings of the mount. Does it clear the iron sight? If not, you have to decide which one you want, iron sight or optic. Since you’re mounting a scope and mount you just paid a bucket of money for, that decision seems pretty clear. Take the sight off.

A properly positioned scope gives you the full field of view without the optic banging you in the forehead in recoil.

Next, check that the scope can be properly positioned on the receiver. You want the rear lens of the scope to be just about at the back end of the upper receiver rail. This depends on the amount of eye relief the scope has, but use this as a starting point. Now, if you are familiar with your shooting position (I crawl a stock like there’s no tomorrow) and know that you need a scope in a certain place, go for it. Or, if the scope has a very particular eye relief, then adjust for it.

At this point you’re ready to do some fit-checking.

Snug the mount screws down more than hand tight but not fully torqued. Install the ring tops, and hand-tighten the ring screws. Keep the scope more or less vertical when you do this. Shoulder the rifle and look through the scope. Is the eye relief correct? Do you have to pull back, or stretch forward? If the scope is not in the right place, take note, put the rifle back into the cradle, loosen screws, adjust, tighten and repeat.

The temptation here is to loosen the ring screws “a bit” and then slide the scope back and forth to get it right. Problem is, doing so risks scratching things up and, once loose, there’s no guarantee that you’ll get it right and it will stay put until you tighten it again.

Once you have the proper positioning for the scope, put the rifle back into the cradle and tighten things up.

A quick note: the LaRue mount uses side-by-side ring halves instead of the top-and-bottom ring system. This will require that you do a bit of jiggling to get the ring halves in place on the scope, and the scope on the mount. One way to make it a little easier on yourself is to use one screw on the top of each ring to secure the rings around the scope (but still loosely fitted) before you then insert the bottom screws, which also go through the fins on the base. It saves you a bit of hassle.

MAKING IT TIGHT

Tighten the base screws, bolts and levers. You want the bolts and nuts to be around 30 in. lbs., and the throw levers to require pushing over center about 20 degrees off the receiver. If you can snap them shut without having to push on them, they aren’t tight enough. If you go over center while they are still poking straight out, you’re locking it too tight.

Check the scope reticle again. Make sure it is vertical. Then tighten the ring screws, using an “X” pattern to pull the ring top down evenly. If there are only two screws in each ring, then “X” across the two rings.

Once tight, shoulder the rifle again, and check that eye relief is correct and the reticle is vertical. If there’s a problem, loosen to adjust.

The base screws or bolts should be 30 in. lbs., the ring screws 20 in. lbs. You can easily generate 20 in. lbs. with the provided Allen wrench that came with the rings. You can likewise generate 30 in. lbs. with a handled screw or Allen driver. You do not need to add leverage in the form of a breaker bar, a crescent wrench on the screwdriver shaft as a lever or other such contraptions.

Your hand strength will be sufficient.

GEISSELE SUPER PRECISION

Bill Geissele has a different approach to building gear. He builds what serious customers who have a real need, want. And he makes it so tough even they can’t break it. Once he has all the bugs worked out, he then offers the excess production to the rest of us who aren’t out whacking bad guys as a daily job.

The Super Precision came from a request to make a return-to-zero scope mount that was unbreakable and didn’t bend or pinch scopes. For most of us, most of the time (even the law enforcement among us) return to zero and pinching are non-issues. If you are shooting varmints, and you have had to re-mount your scope, being off an inch or two out on the prairie dog town isn’t a big deal. You can adjust, and re-zero from the misses. For law enforcement, a patrol carbine that shifts an inch this way or that at 100 yards, when the common distance of engagement is spitting distance is also not an issue. (And can even go unnoticed, unless the shooter is very good.)

The Geissele scope mount has industrial-strength bolts and clamps, and a pair of shear lugs underneath to resist recoil.

This is not to say that other scope mounts are bad. But when you have traveled literally halfway around the world, and the $2,500 scope on your rifle gets busted, you want to know the replacement is zeroed. It is zeroed because you zeroed it back in the USA, and now you can clamp it on and know that your zero will not have shifted an inch at 500 yards or more. Remember, a 1-inch shift at 100 yards translates to a 10-inch shift at 1,000, and that could mean a miss.

The Super Precision is not a QD mount. It clamps via a pair of bolts and shear lugs underneath the mount that keep it firmly in place. The mount also does not bear against the full rail. It is held in the clamp section while the shear lugs keep it centered in the Pic rail. That way, the unavoidable tolerance shifts in the rail don’t affect return to zero.

The Geissele scope mount clamps in four points to minimize irregularities in the receiver rail.

To cut weight, this Geissele is machined out of a block of pre-hardened aluminum.

Installation is easy, and follows the normal scope mount routine. However, you don’t get this level of performance without cost.

The Super Precision is stiff and rugged, but it is also 7.2 ounces. The rings and the scope space are line-bored so the rings will not pinch, bend or otherwise bind the scope. The milled-in pockets and rib on the mount base add stiffness, but that also means a lot more machining. And when you consider that the Super Precision is milled from a single block of 7075-T6 aluminum, that’s a lot of cutting.

If you want a Super Precision, tell Geissele what scope and rifle (5.56 or 7.62) you have and they will make you one. It will set your credit card back between $350 and $400.

QD ADJUSTMENTS

The throw levers on the various QD mounts are there for a reason: to get the scope off fast, if you have to. You see, while a scope may clear your rear BUIS, it occupies the space needed by the BUIS to pop up into position. You can’t lift the rear iron with the scope in place. I had an occasion to use a QD mount in a tactical rifle class. We were in the middle of an exercise when the rain came and we didn’t stop. The rain turned into a downpour and it got so bad I couldn’t see through my red-dot optic. So I pried it off and used the iron sights.

The whole point of a QD mount is “quick” and if you have to use a crowbar to pry the thing open, it's too tight. How to adjust? That depends on the brand.

LARUE

Ever notice that your LaRue QD mount comes with a little flat socket wrench? Of course you did, you have a drawer full of them, one for each mount. And you’ve never used them, right? One of these days you’re going to run into an upper receiver that has a slightly off-spec rail. The LaRue will be too loose or too tight.

A loose fit is when the lever turns down to the rail position without really needing any force. The mount may even be a bit loose on the rail. On the other hand, it’s too tight if the lever has to be hammered or forced flat against the rail. An overly tight lever fit may (usually does) require a screwdriver or some other tool to pry open.

You want your throw-lever to hit the cam-over point at the angle of the lever on the right, not the lever on the left.

To adjust the fit, use the little wrench. Too loose? Open the lever, and then press until it goes to about 20-30 degrees off of the rail. Hold it there with one hand while you employ the wrench to turn the nut on top of the mount clockwise. If the mount has been in use for a while, or has been sitting on the shelf for a long time, you can put a drop of oil in the lube indication place on the mount. Tighten a quarter turn and try to close the lever. If it closes easily, open it, give the nut another quarter turn and retry the lever.

For an excessively tight fit, do the opposite; turn the nut counter-clockwise.

The objective is to make the lever go over center at the 20-30 degree point and still be tight enough that you can’t get the lever open with your fingers alone. Yet if you have to use a pry-bar, it is too tight.

AMERICAN DEFENSE

American Defense takes a different approach. If you look at the far side of the throw levers on this mount, you’ll see a hex-head nut in a recessed socket. Notice the screwdriver slot in the nut.

To adjust the lever tightness on the LaRue mount, use the supplied wrench.

To adjust the QD mount fit, open the lever and lift until it is perpendicular to the mount base. Then push on the lever. On the other side of the mount base, the nut that is attached to the throw lever screw gets lifted out of the socket. To tighten, rotate the nut clockwise. To loosen, counter-clockwise.

If your lever fit is too loose or too tight, open, press and rotate the hex nut ¹⁄₁₆ of a turn. Ease up on the lever, and let the hex nut fit back into the socket. Check the fit of the throw lever. Repeat until you have the fit you want.

And while you’re at it, remember that the American Defense mount’s lever has a locking tab built in. If you don’t press the tab in, you can’t swing the lever open.

Once you have adjusted a particular QD scope mount to a correct fit on a particular receiver, it is fitted to that receiver. If that receiver required your mount be tightened to fit, then that mount will in all likelihood be too tight on your other receivers. Ditto one that had to be loosened. If that is the case, then you just created a dedicated QD mount for that rifle.

Me, I swap QD-mounted scopes between ARs so often that I simply adjust each in turn and don’t worry about making them all fit. If a particular scope and mount are to be fitted to a rifle and left there for a long period of time, I simply don’t swap it.

AIMPOINT GETS IT RIGHT

The Aimpoint mount, bought in literal truckloads by the government, along with the Aimpoint red dot sight, features a handy ratchet-style tightening knob. Once you crank the knob tight, the ratchet cams over and clicks to the next setting. You can check tightness without over-tightening and install or remove it with your bare hands. A very clever design.

EOTECH PARTICULARS

The EOTech Holosight uses a clamping bar that is pulled tight with a screw. EOTech tells us not to use Loctite on the screw, but experience tells us differently. The threads are small and fine-pitched. Without a drop of blue Loctite, it is likely that the screw will vibrate loose under use. If you try to tighten the screw without Loctite, you risk stripping the threads.

So, as an old advertising campaign had it, a little dab’ll do ya.

NOT ALL ADJUSTMENTS ARE EQUAL

The current design paradigm for scopes is that the mounts are simple and strong and the adjustments internal. Well, one company takes issue with that. Elcan, maker of the Spectre scopes, has the adjustments built into the mount — an integral part of the optic. It uses a pair of throw levers with which to clamp the scope, and is zeroed via adjustments in the mount, external to the optic.

The advantage is a hell-for-tough adjustment system and completely sealed optic. The downside is that it unavoidably adds bulk. But it is clever, and the glass brilliant.

RED-DOT HEIGHT

In learning to use your AR, you need to understand a concept called “co-witness.” Your red-dot sight is your aiming spot. If you turn on the red-dot, and stand up your folding iron sight, you can look through the scope and see the irons and the red-dot resting perfectly on the top center of the front sight blade.

This has been cause for much frustration in classes. You see, for some reason, when we first started explaining co-witness to students, many of them assumed that when you had a red-dot scope and iron sights, you used them both at the same time.

That is simply wrong.

Co-witness is an administrative step only. If you have a red-dot sight, and it is on, you use it to aim, and ignore the iron sights. If the red-dot does not work, is broken, whatever, you then use the iron sights. You do not use them both at the same time.

Then, why this co-witness subject?

To mount a compact red dot sight, or RDS, you need a sight riser. Samson makes this, meant for the Aimpoint T-1.

The most convenient way to mount an RDS is with a quick detach, or QD mount, such as this Samson.

Well, if you have properly zeroed both your red-dot and your iron sights (by using them each in turn, shooting groups, and adjusting until you are hitting center), you have valuable confirmation. You can turn on the red-dot scope, look through it, and see that the dot rests top-center on the front sight post.

The Aimpoint mount uses a ratcheted knob that prevents over-tightening.

Let’s say your rifle falls out of the rack, slides off the table or gets inadvertently kicked to the ground. Turn on the RDS and check co-witness. If the dot is still top center of the front post, then nothing has been changed. You’re all set. If they don’t, one of them is off. Which one? A zero group fired with either the irons or the red dot will tell you.

Your co-witness can be center or one-third. Look through your red dot scope. If your iron sights are in the center of the scope tube, or field of view, you have a center co-witness. If, however, when you aim comfortably through the RDS, the iron sights are down in the lower half or third of the scope, then you have a one-third co-witness.

Neither is good or bad. Center co-witness facilitates easier transition from dot to irons and back. One-third affords a clearer field of view, since the iron sights aren’t sticking up into your line of sight.

The best place to locate an RDS is around the front of the receiver. Close enough to be seen, far enough not to block your view.

Which you get depends on the height of the pillar for your red-dot. Some come set up, ready to go with a mount as an integral part of the scope. But many now come as an RDS, leaving you to build the clamping plate and pillar to make it work on an AR. (The use of RDS in pistols is becoming much more prevalent, hence this approach, which makes it possible to make an RDS for both AR and pistol.)

If you have a choice, then you have to choose. If you don’t, then you must live with what is available or offered.

RED-DOT LOCATION

Re-dot sights are not meant to be mounted back on the rear edge of the upper receiver. Good red-dot shooting technique requires both eyes open, allowing the dot to float in your field of view. While you look through a magnifying optic, a red-dot is looked through and around — and you see the whole world.

As a result, the common place to mount it is out near the front end of the upper receiver. Some even position it out onto the handguard, but I find that just a bit too far forward. I want it far enough away that it doesn’t command my attention, like a magnifying scope. But I want it close enough that I don’t have to crank the power all the way up to see the dot.

CHAPTER 7
TRIGGERS

The trigger is your “go button” for fun and defense. It is also the safety lever, something a lot of people have trouble grasping. The concept, not the lever. There is also a lot of hand wringing and concern that the trigger on an AR is too heavy. The military has some interesting acceptance standards. The allowable trigger pull on the M16/M4 is no lower than 5.5 pounds in all versions. Current M16A2, M16A4 and M4 triggers are allowed to be as high as 8.5 pounds, while the M16A3 and M4A1 may push 9.5 pounds.

Ouch.

And yet, I have used rack-grade AR variants of all sizes, with iron sights, to shoot clean scores on the Army pop-up course, the RETS. It includes shots out to 300 meters. But there is a definite improvement in shooting ability with a good trigger. So lots and lots of shooters look to a replacement trigger to solve their problems. Alas, it isn’t quite that easy. But it does help. However, before we get into the replacement trigger section of this chapter, we’ll spend some time explaining how to properly assemble, install and adjust (if any adjustment is possible) the regular trigger system.

Disconnectors from different makers. Notice the variance in the location, shape and quality of the hooks. Some are simply awful. They will all cause different timing issues on the disconnector release.

HOW DOES THE AR TRIGGER WORK?

The hammer presses directly, by means of its sear notch, on the front corner of the trigger. Your finger pulls the trigger, which pivots around the trigger pin. This in turn pulls the trigger corner directly down off of the hammer notch. Well, not quite directly. The angle of the hammer notch is such that the hammer is slightly cocked as you pull the trigger. More on that in a bit.

To understand just how miserable a leverage system this is, here’s an analogy. Go to the nearest door. Turn the knob and open the door. Easy, right? Now close the door and pull on the door before you turn the knob. Oh, that got a lot harder, didn’t it? That’s the same sort of arrangement going on in your trigger setup. The trigger has to pull the corner down across the surface of the hammer notch while a lateral load is being applied.

And that is why so many people spend so much time trying to reduce the toolmarks on those surfaces, because the lateral load is in effect magnified by each tool mark.

You can see all this if you install the Brownells trigger fixture on your lower receiver (don’t forget the dry-fire block) so you can watch the parts, without the lower receiver walls in the way.

MIL-SPEC AND NICER

The military trigger on the AR platform is what’s known as a “single stage” trigger. That is, the trigger movement engages the hammer sear directly. It’s also known as a Class One lever. The force applied, and the force exerted, are on opposite sides of the fulcrum, the pivot point. This means that the calculation of force needed is simple. If the distances are the same, then the movement of the effort and load are the same, in distance and work. If the effort side of the lever (the trigger) is twice as far from the fulcrum as the load, the force needed is half, but the distance required to travel is twice as much.

This is also known as a simple lever.

Archimedes knew this when he explained that if he had a place to stand, he could move the earth. Well, he’d also have needed a fulcrum, but when you are boasting, simpler is better.

The engagement surfaces of the trigger and hammer, known as the sear, have a bit more to do with this than might be obvious. The surface of the hammer notch is at an angle to the lever of the trigger, the trigger axis. Also, the front face of the trigger is tilted to the axis of the trigger lever. The result is, if any force less than the total needed to release the hammer is applied, then released, the surfaces cam back to the starting point.

This is the correct installation of the hammer spring. Do it any other way and you will have problems

Let’s assume you have a 6-pound trigger pull on your AR. If you apply 6 pounds, it fires. If you apply 4 pounds, and then let go, you’ll still need 6 pounds next time you pull the trigger. If the engagement surfaces were perpendicular to the axis of the trigger, applying 4 pounds and releasing would result in the trigger and hammer remaining stationary. The next pull would require only the additional 2 pounds.

You don’t have to be obsessed with safety in order to understand how that would be bad. So, the military insisted on the trigger camming back to zero when let go. If you adjust the trigger pull on your AR, you must not change that feature. The mil-spec trigger, as-is, often comes in at the minimum-allowable pull — 5.5 pounds. Which is pretty good, really. Now, if you’re comparing it to a match-conditioned Garand, you’re comparing apples to cinder blocks.

The Garand has what is known as a two-stage trigger. Designed by John Moses Browning (it seems like every time you turn around, Browning was already there) the trigger is another simple lever, with a twist; it has an extra spring-loaded arm. That arm provides the extra force needed to keep the sear surfaces fully engaged.

One way to assemble the lower is to simply shove the hammer in last so the geometry of the assembly holds it in place. This gets it close enough, but still not perfectly aligned.

The trigger with the disconnector properly installed.

Why did the military, and Armalite in the 1950s, feel the design they had was better? I don’t know, but while some feel it is better, or worse, and both camps disagree over this, it is what it is. And the AR trigger is good enough to do what you need. In the modern era, there are also companies who have taken the design, refined the geometry and then surface-treated the parts. A precision-ground AR mil-spec designed trigger, given a high tech low-friction coating, can be surprisingly good — more durable than some two-stage triggers. But, we’ll cover the two-stage triggers in more detail when we get there.

MIL-SPEC ASSEMBLY

Let’s start from a bare lower receiver, at least bare in that it doesn’t have any internals. Why? Because getting it apart isn’t too difficult and a lot of people seem to think that they must start with the lower empty because they are assembling from a kit or pile of parts. So, we’ll start from a pile of parts.

The trigger and hammer pivot pins come in two flavors, small and large pin. The large-pin lowers are from Colt, made back when Colt was not really sure they wanted to actually be in the gun business. These pins have a diameter of 0.170 inches. Small-pin lowers have mil-spec diameter pins sized 0.154 inches. (This is entirely separate from “large-pin” Colt lower front takedown pins, which are larger than mil-spec. Colt was so weird, for so long.)

The trigger and hammer pins are identical and interchangeable; they are not directional. That is, either end can go into the receiver first from either side. They have two grooves that engage the J-spring in the hammer and hammer spring leg to keep the pins in place in the lower.

Install the trigger spring in the trigger. Position the front loop up underneath the trigger nose, not down on the trigger bow. The spring is tough, so you can bend it quite a bit to make it fit on the trigger. It isn’t indestructible, you can break it, but not easily.

Insert the disconnector spring into the seat in the trigger groove. I know, this is the first we’ve talked of disconnectors, but we’re building from a pile of parts, remember? We’ll cover the disconnector in a bit, but for now stuff the spring in there. Be sure to attach the larger spring loop to the trigger so it stays put. If it falls out, try the other end. If it falls out either way, curse the parts supplier for packing a cheap disconnector spring in the bag and promise yourself you’ll get a proper one later.

Place the trigger in the lower, pushing the first pin across. You want to have a light touch here. The trigger tunnel through which the pin passes has two sharp corners. If you jam the pin in, and hit the corners, you’ll mar the pin. It won’t fit. If you hammer it in, you can damage it. You probably won’t damage the trigger, it is too tough. But the real crime will be when you finish hammering the marred pin into the far side of the receiver. That will chew up the hole, render your receiver inoperable and cost you a new lower. So have a light touch. If it won’t go in by hand, do not pick up a hammer. Find out why.

Some lowers come with the hammer and trigger pin holes drilled to the minimum diameter. Anodizing, the process that makes aluminum tough, causes the surface to grow. A minimum diameter hole, once anodized, becomes below minimum. The pin, if it is near the max allowed diameter, may be a tough fit, even without the trigger to wrestle with. Oil the receiver holes, work the pin in and out a few times and see if you can wear down the high spots. If nothing else, you now know how much force is normal.

Back to assembly. Push the pin in until it captures the trigger, but not past the disconnector slot. Use it as a slave pin. Now push the disconnector down into the slot. Rotate the lower, looking through the hole to check alignment. Move the disconnector around until it lines up with the pin and push the pin across.

Insert the selector lever. Again, first mention. You need a safety/selector. Some lowers (and this is not a brand-by-brand, but a lower-by-lower thing) won’t let you install the safety after the trigger is in. And some won’t let you install the trigger after the safety is in. You’ll have to try the two on your lower and see. Some don’t care: you can install one, then the other, either way. Lucky you.

If the selector fits, great. Pull it back out and set it aside. If it won’t come out, remove the trigger pin and, with the trigger still in the lower, push your selector across. Then re-install the trigger pin. You’ll have to continue with the lever in place. Once you get the hang of this particular dance it gets easy.

With the trigger and disconnector in place, install the hammer spring so the bow is flat to the back of the hammer. Be sure the hammer spring loop bases are forward of the boss on which they ride, not behind. The hammer spring, like the trigger spring, is made tough to withstand bending and to ensure it fits.

Installing the hammer is something those with big thumbs will hate. There are two methods I know of, short of fixtures: self-cocking and thumb-trapping.

The self-cocking method is, hook the hammer spring legs over the trigger pin, with the legs outside of the trigger spring loops. (You always want the legs outside of the loops.) Push the hammer down into the lower, and angle it back into the cocked position. In many lowers, the hammer sear will engage the trigger nose and the hammer will wedge itself into place in the lower. Insert the hammer pin and press it across.

Alas, in too many instances, the hammer stays cocked only until you move it to insert the pin, and then it hurls itself across the room. That’s amusing for the first few times, or until you happen to be looking at it. Trust me on this one, only in romance novels and pirate movies do the ladies get a crush on a man wearing an eye-patch. Don’t lean over the lower, always wear safety glasses and follow my method if your lower does this even once.

The thumb-trap method is as follows: pinch the hammer between thumb and forefinger. Hook the legs over the pin, outside of the loops. Press the hammer into the lower, keeping it upright in the fired position. As it travels into the lower, slide your forefinger into the magazine well — pinching the hammer in place. It can’t escape, but it can cause your thumb and finger a certain amount of discomfort.

To assemble the hammer, with everything else in place, I use the pinch method.

Hold the lower and trapped hammer in one hand, picking up the hammer pin with your other. Adjust the alignment while holding the hammer and moving it to get the pin started when the holes line up. Now stop pinching the hammer. Once in, turn it over, press the pin across, then use the hammer as a lever to align the pin with the second hole, and you’re ready to press it through and flush.

You’ve assembled the hammer and trigger, but you are only halfway done.

Before you proceed any further, be aware of one detail. Don’t let the hammer fall, full-force, with the upper and lower apart. Otherwise you risk damaging the lower. So either do all the testing work with your thumb in the path of the hammer or use a dry-fire block from Brownells.

Cock the hammer. Does it stay in place? Good. (If not, there is either something wrong with your assembly or the parts are awesomely bad.) With thumb in the hammer path, press the trigger. Does the hammer fall? Good. Cock the hammer again and rotate the safety on. Try dry-firing. If it doesn’t fire, you are well on your way to completion. If, however, the safety, when correctly installed, does not keep the hammer from falling when you press the trigger, you have a serious problem.

QUICK SAFETY BRIEFING

The safety/selector works by blocking the upward movement of the rear of the trigger. Look at the safety, noting a milled flat. This is the clearance for the trigger when depressed to fire. The safety rotates a quarter-turn, and presents the edge of that shelf, the barrel of the cylinder, to the trigger. This blocks upward movement, keeping the rifle from firing.

If your rifle will fire when on safe, then the rear of the trigger is too low. You can’t build up the safety, it has to pass through the holes in the lower receiver. You can replace the trigger with one that goes on safe when rotated or build up the rear of the trigger. Back in the good ol' days, when parts were hard to come by and were fabulously crappy, I silver-soldered shims onto the rear of the trigger, carefully filing them down to proper size.

Nowadays, I’d simply try the next trigger in the bin or send the trigger back, after checking to make sure it wasn’t the receiver that was at fault. If it’s the receiver, send that puppy back, pronto.

With the Brownells fixture, you get a clear view of the parts and how they function.

One way to check is to use a properly working set of parts from another rifle. If they work in the new lower, then the fault lies with the new parts. If the proper parts now fail in the new receiver, then chances are the new receiver is the problem.

One of the good things about having a properly functioning rifle on hand when building a new one is the opportunity to do checks like that.

Let’s assume yours works fine, and get on with the task.

DISCONNECTOR CHECK

The disconnector is the flat gizmo that keeps you out of prison. To check it, hold the lower, with thumb in front of the hammer, and dry-fire. Now, while continuing to hold the trigger back, press the hammer back to cock it. Notice that it now is hooked on the disconnector, not the trigger nose. As long as you hold the trigger back, the hammer is trapped. That’s what keeps it from running away in full cyclic mode, expending all your ammo in one exciting, nerve-wracking, expensive and unlawful few seconds.

With your thumb still in the path of the hammer, slowly ease up on trigger pressure. You’ll see the parrot’s beak of the hammer slide off of the disconnector nose and let go. If the disconnector is properly timed, the hammer will be captured by the trigger nose and you’re good to go.

The disconnector spring, in an M16 trigger (the open end of the rear tells us that) and ready for a disconnector.

What is meant by disconnector timing? As you ease up on the trigger, it rotates, slowly coming to the point where the disconnector lets go of the hammer. The trigger nose, or sear, rises into the path of the hammer notch. If the trigger/disconnector lets go of the hammer too early, the trigger will not have lifted high enough to catch the hammer. Two shots will be fired — one when you pull and one when you release. Some rifles have an early timed disconnector, but their owners don’t know it. They don’t know it because they have only ever fired by pulling the trigger back, and then releasing it as quickly as possible. The trigger spring, in full power, has enough oomph to push the sear into the hammer notch path. However, when the same shooter, with the same rifle, tries to do accuracy work off the bench, they may ease the trigger forward. Holding the trigger back from full release, the early timing causes the hammer notch to miss, or bounce, over the trigger and fire. Oops.

At the opposite end, a late disconnector releases only when the trigger has fully risen up into the hammer notch path. You’d think, “Cool, late is what I want.” No, you don’t. You see, the engagement surfaces of the hammer and disconnector may have machine tool and stamping marks on them.

The disconnector in particular is a source of misery. You see, it is produced by a process known as fineblanking. This is a refinement of the punching process, which produces products with a cleaner edge. However “cleaner” is the operative word. The end result is a relatively straight, relatively clean-edged part that requires no further treatment besides hardening and surface finishing. In some applications (not necessarily firearms), even the hardening process isn’t needed, depending on the alloy used and the application. The result is a disconnector hook that is not correctly shaped with a rough underside surface.

The hammer, meanwhile, is cast and then machined. The hammer’s hook can have what is known as a wire-edge, where the last cut caused a tiny curl of steel to form on its end.

Combine the wide edge and the rough surface of the disconnector with a late-timed setup, and you can have a disconnector that never lets go.

So, ideally you want a disconnector that releases the hammer past the half-way point of trigger movement, but does so no matter how slowly you ease off on the trigger.

DISCONNECTOR TIMING

Changing early disconnector timing is easy. The disconnector is timed to the trigger by its engagement with the trigger underneath the front tab of the disconnector — the angle that juts forward, below the hook. The underside of that surface is your target. A clean, sharp file is all you need. Typically, disconnectors are made of 4130 steel, which is hardenable, but except for the top-tier (and I hated typing that, but here it does apply) manufacturers, it is usually only surface-hardened.

Simply take the disconnector out, turn it upside down and clamp it into your bench vise. Take a couple of passes along that surface to clean it up — the rough surface might be a big part of your problem — and to remove metal to adjust the surface location.

Top, the M16 disconnector, bottom the AR-15 semi-auto disconnector. Grind off the tail of the M16 disconnector, and you have an AR version, which is exactly what the factory does.

Reinstall the disconnector and check timing. You’ll probably find it has changed a little.

Repeat until the disconnector releases late of the halfway point, but not at the end of the trigger movement. Wait, you aren’t done. Pull the disconnector out one last time, knocking the burrs off the edges with your file, making sure the disconnector moves freely in the trigger slot. You can also cold-blue the surface if you want, but no one will notice. While you have the disconnector out, gently hone the undersurface of the hook with a medium coarse stone. You are not looking to change the timing, just smooth the surface if it is rough. While you’re at it, look at the hammer hook, and see if there’s a wire edge to it. If so, stone that, too.

What if the disconnector is late? My first choice would be to swap disconnectors until one is found that isn’t late. However, if you have only one, then you can adjust timing on a late disconnector. Your target here is not the underside of the disconnector nose, but its tip. The underside can only make it smoother, not change the timing. By trimming the disconnector nose you allow it to release the hammer sooner.

Use a stone to smooth under the disconnector nose and, if there is one, the wire edge from the hammer. A simple smoothing over of these could solve the problem of a late-timed disconnector.

If not, then you have to adjust the disconnector nose tip. You must take more care here than in filing to correct an early release. The amount of metal removal needed to correct late timing is much less than the amount needed to correct early timing. File just a tiny amount, reinstall and check timing, repeating process until correct.

Once the disconnector is timed and the safety passes its check, you’re done with the mil-spec trigger installation. But what if the mil-spec trigger is too heavy?

TUNING THE MIL-SPEC TRIGGER

Some claim you should not polish, stone or otherwise adjust the mil-spec trigger, because it is soft inside and will wear quickly if you cut though the outer layer. As with many things, this does have a kernel of truth, but for the most part it isn’t the case.

I asked an industry insider who makes mil-spec parts about this. The response surprised me. The hammer is composed of an alloy known as 8620. This is a chrome-moly-nickel alloy that takes carburizing well. 8620 is known for its very good casting characteristics. That the hammer and trigger are cast should not be seen as a defect. The casting does not usually need to be heat treated, as 8620 is an air-hardening alloy. That means it does not have to be quenched, only air cooled, which causes the crystalline structure to form in a hardened state.

Once cooled, the parts are treated for carburizing, introducing additional carbon into the surface for extra hardness and wear durability. This hard surface, called “case hardened” in the old days, is listed in the mil-spec as being 0.014 to 0.018 inches thick. The parts are parkerized for corrosion resistance and then we come to the dicey part. The hammer hook and trigger face are machined or ground to create the engagement surfaces. This can remove half or more of the hardened layer, leaving a much thinner hardened layer on the engagement surfaces.

Unless you are using power tools, you will be hard pressed to polish through .014 inches of hardened steel. However, if only half that amount is left, say .007, the chance of problems increases. How thick is .007 inches? That crisp new dollar bill in your pocket is .0045 inches thick. So, just under two of those. Ouch.

It is possible for someone with a good stoning fixture, steady hands and much patience to clean off the toolmarks on the engagement surfaces to improve the trigger pull. But if one thing goes wrong here, you have a rifle that doubles — firing two shots with one pull of the trigger.

As a result, I can’t in good conscience recommend that you go polishing on the hammer hook and trigger nose of your AR. Why? What can go wrong? For one, you might change the negative angles on them. Those are the angles that cause return to full engagement if you pull the trigger part way and then release. Second, if you do go too far, and end up with incorrectly polished parts, you’ll have created a two-shot or more AR. And that, ladies and gentlemen, is the exact legal definition of a machine gun.

Which is the main reason we don’t go messing around with the mil-spec parts. If the parts are all original, and unaltered, and you have a rifle that occasionally goes burp, then you have a solid explanation: the parts are bad. If you’ve polished, stoned, filed, ground or otherwise worked on them, then it’s all on you. Good luck with that, because people have been sent to prison for just that very thing.

Can you improve the trigger pull with some careful polishing? Yes, but do not expect anything magical as a result. If you’re careful you can remove the grittiness, but you are not going to make an 8-pound trigger a 3-pound one with some polishing. No, for that you’ll have to replace the parts with something non-mil-spec.

PROPER TUNING, MIL-SPEC TRIGGERS

The best solution to tuning mil-spec triggers is to swap out the crusty USGI parts for a hammer and trigger that have been made with the engagement surfaces properly polished. If you want to do more than that, you can reduce the hammer mass or the hammer spring power.

Colt took the first approach, producing a match trigger that was a simple stub of the usual GI hammer. They chopped off the hook on the back, leaving the upright stick as the hammer. This cut the mass of the hammer in half, which increased speed, reduced lock time and retained primer impact force. (You might have a problem with really hard, military surplus primers. However, the supply of those has long been used up in surplus ammo.)

This is the notch on the upper corner of the hammer, which Colt designed to prevent hammer-follow full-auto fire.

In the early days, I took this approach myself. I had the happy situation of a set of bins filled with hammers, triggers and disconnectors and I could swap them around until I found a set that worked well. For the match rifles, I used a mill or cutoff wheel, making the hammer just an upright vestige of itself.

However, lightening the hammer does not address the weight of trigger pull. So, I figured out a way to bend the existing hammer spring to lighten the lateral force on the engagement surfaces. Now you can simply buy lighter-power hammer springs from many sources (I suggest Brownells) and use those.

Don’t tinker with the trigger spring. It would seem that taking the force directly out of the trigger pull would have better effect. Yes, but the trigger spring is also the trigger return spring, and by reducing its strength, you slow its return up into the path of the hammer notch. It’s true that a properly timed disconnector will not release the hammer until the trigger nose is in the path of the hammer notch. But I like insurance.

Also, I first tried the reduced hammer spring approach, it worked and worked well, so I never bothered with the trigger spring.

REPLACEMENT TRIGGERS

For a proper trigger pull, you need to replace everything with the exception perhaps of the safety. Trigger replacements come in four different versions — improved mil-spec, improved non-mil-spec, two-stage and self-contained or packet triggers. The packet triggers can be had in either single- or two-stage.

Black Rain Ordnance also makes a packet trigger assembly.

ONE MORE COLT HEADACHE

Added to the other Colt problems is the trigger pin issue. In order to prevent the use of full-auto parts (not that there was an epidemic of such actually happening) Colt tried to adopt a new “civilian-only” standard. The regular, mil-spec trigger and hammer pins are a nominal 0.154 inches in diameter. Colt made the new standard 0.170-inch pins.

New rifles would not accept the old pins, and old rifles were beyond Colt’s control. Well, if you have one of those old Colts, your only choice is to use large pin components. Back in the day, that meant you were stuck with whatever God-awful crap Colt decided to put into a so-called civilian rifle, and any replacement parts you might track down were made in the same place … Colt.

Now days you have choices. Not as many as you’d have had with rifles using the regular small pins, but you do have choices.

The Brownells dry-fire, trigger-adjustment and learning fixture. That was too long a name, but that’s what it does.

IMPROVED MIL-SPEC

Improved mil-spec are hammer/trigger sets (some come with disconnectors, some don’t) that have been built on the same pattern but with greater care. The surfaces might be ground and polished before hardening. The parts might be plated with a high tech corrosion-protection and lubricity plating. They can be fully machined from bar stock, rather than castings that have been touched up on engagement surfaces.

Examples include the JP Enterprises original trigger, parts that started the design process looking like USGI, with added adjustment screws to let you tune in sear engagement, overtravel and the ability to swap spring strengths.

IMPROVED NON-MIL-SPEC

Improved non-mil-spec triggers are epitomized by Geissele, a company that went even further. While most Geissele triggers are non-adjustable, they took the USGI design, tightened the operating dimensions, made the hammer, trigger and disconnectors out of better steel and precision ground the engagement surfaces. Interestingly, despite my classifying them as non-mil-spec (due to the appearance, dimensions and tolerances) they came about because military special ops wanted better triggers.

TWO-STAGE

The disconnector does double duty on a two-stage trigger. It first captures the hammer on the cocking stroke. Then it acts as a spring-loaded trigger stop to control trigger pull at a low level, while keeping the hammer fully controlled. The original comes to us from John Moses Browning and the Auto 5 shotgun. Since then it has been adopted, stolen and adapted to a host of rifles and shotguns, from the Remington Model 8 to the M1 Garand and the AK-47.

Brownells fixture with ALG trigger parts installed.

How the two-stage trigger works. When the action cocks the hammer, the rear hook of the hammer catches on the disconnector.

To see how it works, make sure your gun is unloaded. Start with the hammer cocked, safety off, and your finger depressing the trigger. Note the upside-down “T” at the hammer’s engagement notches. The trigger has a pair of hooks. The front hook is the trigger sear, the rearward hook the disconnector and second step. An important point: these two sear surfaces are not the same distance from the trigger pivot, the trigger pin. The disconnector hook is slightly higher and farther from the pivot point.

As you release the trigger, the disconnector "hands off” the hammer from the rear hook to the front hook.

When you pull the trigger, the hammer hooks on the forward trigger sear and, as you pull, the trigger sear slides forward, toward release. But, once it gets halfway there (or so) the rear arm of the hammer T bumps up against the disconnector.

The disconnector is hinged in the trigger (not on the trigger pivot point) and has its own spring. In order for the trigger to keep moving and release the hammer, it must pivot the disconnector back out of the way. This is the second stage of the two-stage trigger system.

This means you can have a very light, smooth, even delicate engagement between the trigger sear and the hammer sear, and the trigger pull weight will be regulated by the force of the disconnector spring pushing in the second stage.

You complete the pull, the hammer is released and the rifle fires. Your finger completes the pull, remaining there as the hammer re-cocks.

When the hammer comes back in cocking, the trigger sear is out of the way. But the disconnector, pushed by its own spring, has pivoted forward and the rear arm of the hammer T now hooks onto the disconnector.

When you release the trigger, the disconnector pivots back, releasing the hammer T. But before the disconnector can release, the trigger hook slips over the hammer hook and the disconnector hands off the hammer to the trigger.

You are now back to where you started.

A two-stage trigger pull feels different than a single stage. As you pull a single-stage trigger, the required weight increases in a more-or-less smooth rate until you reach the release point and the hammer falls.

As you pull the trigger, the first stage is the hammer hook sliding on the sear. The second stage begins when the rear of the hammer hits the disconnector. At this point, the second stage pull is applied against the disconnector spring.

In a two-stage trigger, you press back with half the force you need for release (more or less) until you feel a mechanical stop. That’s the disconnector nose bumping the hammer T. Then you add the rest of the pull weight for release. Except, it doesn’t feel like you have to add weight since your trigger finger is already pulling a certain weight and your brain and trigger finger accept that as normal, and thus, zero. The extra weight is all you feel.

As a result, let’s compare two 5-pound trigger pulls. On the single-stage, you pull and pull and, once you get to 5 pounds, the hammer falls. On the two-stage, you pull at 2 pounds until you hit the stop. Then your brain forgets those 2 pounds and you only feel the next 3 pounds needed to push the disconnector back.

In effect, the two-stage trigger has the mechanical safety of a 5-pound trigger, while feeling like a 3-pound trigger.

It is important to remember that on a single-stage trigger, disconnector geometry is what controls early or late timing. The two-stage trigger also has a geometric determinant of timing, but the parts are so much closer to each other, it's simpler for manufacturers to maintain correct timing. Also, the parts maker produces all of the parts. In the single-stage design, the trigger and the disconnector makers may not be within a thousand miles of each other. Two-stage triggers are made as complete sets, in the same shop, thus it's very unlikely to find an incorrectly timed disconnector in such a design.

Single-stage trigger pull weight is determined both by the strength of the trigger spring and the smoothness of the engagement surfaces. The single-stage requires a strong trigger spring in order to keep the trigger lifting quickly enough to intercept the hammer notch. In a two-stage trigger, while the geometry has to be correct, the force of the disconnector spring determines pull weight. The disconnector spring does not have to be strong to ensure hammer notch interception.

PACKET TRIGGERS

One of the problems with the AR-15 is that it has been made by a slew of manufacturers. That’s good, in that a wide industrial base makes it difficult to put a crimp on things. Were AR-15s only being made by Colt, and only being supplied by one aluminum forging shop, the defense efforts of the US could screech to a halt from the slightest disruption in supply chain.

But unless the myriad of shops that make ARs all have the same blueprints or CAD/CAM data, and unless they are all regularly inspected, dimensions will wander. Trigger pull can vary depending on the particular lower into which the parts are dropped. No, there is no list of good, average and bad lowers. Rest assured, though, that for the big-name makers, dimensions do wander. The locations of the hammer and trigger holes can vary simply because a shop doesn’t have the actual USGI blueprints. They may have taken in lowers made by Colt (who else?) and measured them to come up with as-close-as-they-can dimensions.

If dimensions vary by a few thousandths, that difference can have a big impact on felt trigger pull.

Packet triggers — which can be either single- or two-stage — avoid these issues. Think of a package with all the working parts in a self-contained envelope, one that does not depend on pin hole location accuracy, and then every single one you make will have the same trigger pull. This voids the problem of off-center pin holes. The packet utilizes tubes in which the hammer and trigger/disconnector pivot. The tube’s hole is larger than the regular hammer and trigger pins. The packet essentially floats on the two pins, finding its own center. The clever makers (and they are all clever, one way or another) use spring clips to catch the grooves in the standard pins, which keeps the packet in place and the pins from falling out.

Since the hammer and trigger pivot on the tubes, and the tubes are fixed to the packet, the maker has absolute control over the dimensions. In such a situation, it is possible to make the trigger pull in the packet pretty much anything you want, within the limits of material and design.

The main thing to remember about the various packet designs is, they are not user-serviceable. They were not designed to be disassembled by you. Your maintenance will consist only of prying the packet out of an encrusted jacket of carbon, scrubbing, hosing, degreasing, scrubbing some more, oiling and re-installing after you’ve shoveled the carbon out of the lower.

You can't adjust trigger weight, overtravel, etc. All that has been done for you, that’s why you bought a packet-design trigger system. If you wanted one that had a half-pound less weight, you should have selected that one from the drop-down menu when you ordered it.

IMPROVED MIL-SPEC

The installation of improved mil-spec triggers is exactly like that of the mil-spec variety, with one caveat. If you do any filing, stoning or other changes, you’ll have voided the warranty. If you take a precision-machined, plated trigger system, and drop it into your lower, and find it does not work properly, the odds are good it is your lower that is at fault.

There are no lack of improved mil-spec parts, and you can find them pretty much everywhere.

IMPROVED NON-MIL-SPEC

ALG DEFENSE QMS

The Quality Mil-Spec trigger, or QMS in ALG-speak, is at first blush just a set of mil-spec parts. However, ALG has taken the basic forging/casting and precision machined the engagement surfaces of the trigger and hammer. This produces a trigger with a weight no less than mil-spec (a rated 5.5 pounds minimum) but eliminates the grit, creep, toolmarks and other problems that a fully mil-spec (and thus lowest bidder) trigger pull presents.

ALG Defense offers a box-stock trigger, but with a cleaner pull.

This comes to you for the amazing price of $49.00 (2016). That’s pretty much what the one-stock mil-spec parts would cost if you were to haul yourself off to the next gun show and peruse the bins of parts on the tables there.

So save yourself the hassle and just get the ALG if you need a box-stock looking parts set that delivers a clean trigger pull.

ALG DEFENSE ACT

If you take ALG’s QMS, clean and smooth the engagement surfaces and differentially plate the parts, the end result is the Advanced Combat Trigger, or ACT. While the pull weight is not reduced below mil-spec, its smoothness will fool you into thinking that is the case. Dry-fire it, and you’ll swear it’s a 4-pound trigger. Then go and hang some NRA weights on it and find that it holds 5.5 pounds.

The ALG Defense Advanced Combat Trigger. The same parts as GI, but the sear surfaces are ground to a better finish and are plated.

The trigger is given a nickel-boron coating, which imparts impressive wear resistance, in addition to being harder than an IRS auditor’s heart. The hammer is given a nickel-Teflon plating. The Ni-PTFE coating, while not as hard as the nickel-boron, has a pleasing lubricity, easing the trigger pull. As a bonus, ALG plates the disconnector and the pivot pins in the nickel-Teflon as well.

If your agency or department doesn’t allow non-GI parts, that’s a problem, I’ll admit. But, what they really are getting at (and the regs may even be written this way) is no external modifications, or modifications that require a trained armorer.

The big advantage to nickel-boron coating is that it can be painted. You can spray paint the trigger bow a flat black and it will not be externally modified. Just be sure to mask the trigger so you don’t paint the sear.

The Advanced Combat Trigger gives you a clean, crisp 5.5 pounds minimum pull, yet from the outside looks like a standard trigger. In fact, it would be the standard trigger today, if the Neanderthals in DoD had spent the last half-century actually improving the M16.

ALEXANDER ARMS

Alexander arms improves the single-stage. Not only is the hammer lightened, the disconnector skeletonized, and the surfaces polished, but there are engagement and overtravel screws for adjustments.

Alexander takes the single-stage trigger and improves it. First, the engagement surfaces are cut and polished to perfection. Then unessential mass is cut away from a standard hammer. A lightened hammer reduces lock time as the spring has less mass to accelerate. The impact of the hammer on the firing pin is less, reducing vibration and error-inducing problems. And the firing pin moves faster (law of conservation of momentum), reducing lock time.

There are two adjustments, one for sear engagement, the other for overtravel. They are adjusted in the same manner as the JP trigger. You have a choice of standard or blade trigger bow.

JP ENTERPRISES

The original JP trigger is a highly modified single-stage trigger that also looks like a regular GI part, but with a closer examination exudes good engineering. The JPFC-1 is a refined single-stage that can be tuned to produce a very good, even exemplary competition trigger — especially when combined with a JP speed hammer.

The engagement surfaces have been precision ground and the angles have been adjusted, reduced to the cam-on-trigger-pull geometry of the USGI engagement surfaces. Select the appropriate spring weights and engagement dimensions and you can make a super competition trigger, or a very good and useable one for duty or defense.

The JP Enterprises trigger can be installed using their locking pins. If you’ve gone to the trouble of making it perfect, you should make sure it stays that way.

But to achieve this you must tune the parts to each other in the receiver in which they will be used. There is no “one tune fits them all” solution.

The adjustment screws on the trigger allow you to fine tune sear engagement, overtravel, and disconnector timing. The springs adjust pull weight.

As is usual with JP, the support is overkill. Not only are there complete instructions, but a DVD video and — if all that wasn’t enough — the option of having JP do it for you. As long as you haven’t done any stoning, filing, grinding or other unalterable changes, you can just pack up your lower and the JP parts, ship them off and JP will assemble it for you. It takes a week, they charge a small fee and you have it done right.

The JP Enterprises original trigger: adjustable, a good learning tool and a great product.

Double check as always that the gun is unloaded. Do a preliminary check-fit to make sure all the parts will go into the lower receiver. Your receiver may be machined too narrow, the trigger and hammer might not fit. If everything fits, you can begin.

Install a dry-fire stop in the magazine well, such as the Brownells.

Install the hammer and trigger. Leave the disconnector out for the moment. Cock the hammer. Use the supplied wrench, turning the overtravel screw down until it stops. No matter how hard you press the trigger, the hammer won’t fall. Now, rotate the overtravel screw out (upwards) until it clears the hammer and you can dry-fire.

The original JP trigger has adjustment screws. Located in the front, this is the sear engagement screw.

At this point you have to make a decision. The less overtravel you have, the cleaner, crisper, and all-around better your trigger pull will be. It will also be less forgiving of dust, dirt, crud, carbon build-up and anything else that is determined to get in the way. Also, a minimal no overtravel situation can cause you problems if you fail to reset the trigger crisply.

Remember, the JP trigger is meant as a competition trigger, for 3-Gun and DCM. It is not meant for duty or defensive applications.

Adjust the sear engagement screw. (This is the one in the rear of the trigger.) Cock the hammer. Adjust the sear engagement screw until it pushes the trigger out of engagement and the hammer falls. This is the release point. With the hammer forward, JP recommends that you back the engagement screw from the release point by three-quarters of a turn. They suggest that the absolute minimum for competition use is a half-turn, but I’d add to that. For me, the absolute minimum is three-quarters, and I’m much happier with a full rotation back, for best sear engagement.

Recock the hammer and check the trigger feel. Decide if it meets your standards for competition use. Install and time the disconnector, as we’ve outlined earlier. Except, with the JP trigger, the supplied disconnector isn’t a half-mangled stamping but a precision-machined piece of hardened steel plate. The job should be easier, but you still need to check the timing, correcting any early or late release.

Last, fit the safety. JP ships with the trigger tail machined a bit on the high side. You do not need to remove the hammer. The now-adjusted overtravel and engagement screws keep the trigger exactly where it should be and the hammer will not be a hindrance, except to install and remove as you go to do your filing. If you cannot get the safety to rotate to Safe, then you’re all set. Carefully and gradually file the top deck of the trigger tail until it just clears the safety. The correct fit is achieved when the safety top clicks into place without binding, but with no trigger movement at all once the safety has been applied.

To adjust the weight of the trigger pull, JP offers springs of different strength, color-coded with paint. Adjustable weight ranges from a low of 3.5 pounds, up to the 4.5 pounds required by CMP competition. And as if all that wasn’t enough, JP offers locking hammer and trigger pins. They come with headed screws that you tighten (you can use Loctite if you wish) to make sure the pins don’t move.

TWO-STAGE TRIGGERS

GEISSELE

Geissele (pronounced “guys-lee”) sprang onto the scene making triggers for bearded guys who went to dusty places, there administering justice to unrepentant medieval whackjobs. Once things were made to his — and the professionals' — satisfaction, Geissele marketed triggers to the rest of us. Which works for me.

Geissele makes a demo fixture for their triggers, so you can see how they work and feel the trigger pull for yourself. This is a two-stage trigger.

The company makes 21 different triggers as of this writing, most of which are for the AR in one version or another.

GEISSELE S3G, SUPER 3-GUN

The S3G is a derivative of the Super Select-Fire (SSF) trigger, which Geissele made for special operations teams. That’s right, a machine gun with a target trigger. Actually, you targeted in semi-auto mode and, when you flipped the giggle switch, trigger pull became less an individual event and more a hose on demand option. 3-Gun competition isn’t full-auto, but you can still heat up a rifle quickly. And you have to hit what you are aiming at or your score suffers.

The Geissele Super 3-Gun trigger, ready to drop into your lower receiver.

So, Geissele took the SSF, removed the select-fire knobs and extensions, and produced the two-stage Super 3-Gun from it.

Its trigger pull comes in at right around 4 pounds. You can ease that up if you use a lighter hammer spring, but you wind up increasing lock time.

Aside from changing trigger and/or hammer springs, there is no adjustment in the S3G.

GEISSELE HI-SPEED NM-DMR

For National Match competition and the Designated Marksman program, the military decided during the war in Iraq and Afghanistan that trigger pull matters.

The Geissele Hi-Speed NM-DMR is an adjustable two-stage trigger. Each one comes with detailed instructions. There are a few things that you must attend to and be aware of with this product. It's not a simple drop-in installation.

First, use only the included hammer pin, not the mil-spec GI pin you removed. Also, the Geissele pin is installed from the left side, and its retaining groove must be on the left side of center.

Second, make sure the safety selector blocks the trigger before you start adjusting things. If the lower receiver is off so much that the safety won’t work, you need to be looking at a different rifle, not carving on the Geissele.

And finally, the Geissele trigger needs proper clearance in the lower. Assure correct fit of the lower's oval through which the trigger bow pokes. It is not unusual for the oval to be excessively machined — the specs on this assume a mil-spec trigger, and we know what mil-spec means — such that the Geissele bow contacts the edge of the oval.

The Geissele High-Speed NM Trigger, complete with extra springs, assembly tool and adjustment wrenches.

If there is a problem, it’s a conundrum. The standard gunsmith fitting process is to cut on the cheaper, easily replaceable part, to make things fit. A new lower costs less than a new Geissele. But, the lower is the serial-numbered part, and more difficult to replace if you make a mistake (especially in some jurisdictions).

Me, I’d cut the lower, since aluminum is softer and easier to trim than hardened steel.

Last, follow the instructions for adjusting overtravel and sear engagement. You can remove all the overtravel, but if you do, you pretty much make the rifle useless. Even a change in temperature can mean your no-overtravel situation becomes a … no-travel situation. And, you want to ensure enough sear engagement to keep the rifle drop-safe.

LARUE TACTICAL MBT-2S

The MBT-2S (Meticulously Built Trigger) is crafted from S7 tool steel. As in, take a plate of pre-hardened tool steel and cut triggers, disconnectors and hammers out of it. Then, have the in-house toolmakers assemble and test each one before packing and shipping.

Tool steel is incredibly hard, and wears like … tool steel.

Geissele makes two-stage triggers for all uses and occasions.

As a two-stage trigger, the MBT-2S has an initial pull of 2.5 pounds, followed by a break at 2 pounds more. It is for small-pin lowers only and cannot be adjusted. It comes with pins and springs in a nifty padded shipping can with clear top so you can see exactly what you’re getting.

Installation is simple, and is exactly like that of a mil-spec set of parts — except when you’re done you get a marvelous trigger pull.

MORE PACKET TRIGGERS

The first packet trigger came to us from Chip McCormick Custom, or CMC. It was fabulous. No more tuning, adjusting or fiddling with the disconnector. The trigger pull was what it was, regardless of what lower you installed it in.

There were drawbacks. The stamped sheet steel shell was not always an easy fit in some rifles. Perhaps I have too many legacy guns, made decades ago by people no longer in the business, but in some of them the CMC was a tight fit. (In one, it wouldn’t fit at all.)

One of the very first Chip McCormick packet triggers.

But that was changed a few years ago and the new units are much better. They fit all the current lowers and you have choices. The first choice you need to make is single- or two-stage.

In single-stage, pick a trigger weight, any of four weights, from 3.5 to 6.5 pounds, in full-pound increments (3.5, 4.5, 5.5, 6.5 pounds). Then choose between curved or straight trigger.

For two-stage, choose either 1 pound on the slack and 3 pounds on the pull, or 2 pounds on the slack and 2 on the pull. Curved or straight trigger is the other option here.

WILSON COMBAT TR-TTU

The Wilson Combat Tactical Trigger Unit is a single-stage, semi-auto packet trigger. To install, yank out the old parts. Slide the TR-TTU in, making sure it clears the selector. If it doesn’t, remove the pistol grip. Put in the TR-TTU, placing the selector back. Don’t lose the selector spring and plunger.

One of the big advances that came along when we moved from stamped to machined aluminum shells, was the inclusion of “D” clips. The D clips catch on the grooves in the hammer and trigger pins, keeping them in place.

The Wilson Combat TR-TTU packet trigger.

The hammer, trigger and disconnector are wire-EDM cut; the shell is CNC machined and there are no adjustments. The Wilson Combat trigger comes with hammer and trigger pins, so if you are building from scratch you don’t have to source those as extras. You can use the Wilson parts or the ones you already have. Either will work.

As a bonus, the TR-TTU has a half-cock notch, much like that of the 1911 pistol. If you are worried about a discharge when the rifle is dropped, the Wilson Combat trigger takes care of that. Should the hammer jump the sear when dropped with nothing holding the trigger back, the half-cock notch will catch the hammer without firing.

If the 4 pound weight of the TR-TTU isn’t to your liking, Wilson makes packet triggers in an array of weights and as two-stage variety as well. In all, five different units are available, with weights from 3.5 to 5.75 pounds.

TAC-CON

The Tac-Con trigger is a neat bit of gear. First of all, it is a packet trigger in a machined aluminum shell sporting precision made hammer, trigger and disconnector. The internals are wire-EDM cut from precision-ground pre-hardened stock. The working parts are given a plating of NP3, a nickel-teflon self-lubricating coating. The pin tunnels have built-in “D” clips, hammer and trigger pins held in place by the packet. And the single-stage design provides a clean, crisp 4.5 pound trigger pull.

Tac-Con supplies a packet trigger and a replacement safety.

The third mode of the Tac-Con is a positive reset. The mechanism uses the power of the cycling carrier to reset the hammer-sear engagement, reducing the split time between shots. It isn’t full-auto, and Tac-Con has the letter from the ATF proving it, but it is such a high cyclic rate that someone who didn’t know better would think you had one.

It is a clean, crisp trigger pull, which can make a difference in your scores in a competition.

To install, pull out the old parts, plug in the Tac-Con, make sure it plays well with the safety/selector and doesn’t bind in the lower receiver and you’re done.

AMERICAN GOLD

One of the first, if not the first, packet trigger makers after Chip McCormick, American Gold went with wire-EDM internals and an aluminum shell. To give you an idea of how good it is and how much of a change it can produce in your AR, consider Jerry Miculek. Considered (rightly) to be the best revolver shooter who ever lived, Jerry is also a really good all-around shot, and a serious 3-Gun competitor.

The American Gold packet trigger model that Jerry Miculek used to win the 3-Gun Nationals.

American Gold sent him a trigger to try out. He plugged it into his competition rifle a couple of weeks before an upcoming USPSA 3-Gun Nationals. It made such a difference that he left it in, went to the Nationals, won, and told American Gold they weren’t getting their trigger back.

It’s a packet trigger, installation is easy, as covered earlier.

TIMNEY

Timney has been making replacement triggers for what seems like forever. When a hunter wanted a good trigger on an inexpensive, military surplus rifle, he went to Timney. When taste in rifles shifted from bolt guns to self-loaders, Timney paid attention, releasing a line of AR triggers.

The Timney packet trigger.

Offering both single- and two-stage triggers, the Timney design is consistent across models — a machined aluminum shell with precision wire-EDM cut S7 tool steel parts.

To install, do all the regular steps; pull out the old, check the fit of the trigger to the safety and the trigger clearance oval before putting it back together.

Where the Timney design differs, is in how it secures the packet inside the receiver. Instead of “D” clips on the pin tunnels, set-screws are used to press the packet up, employing the bottom interior of the lower receiver as the push-plate.

The process isn’t difficult. Make sure everything fits, press the Timney down into the receiver and push the hammer and trigger pins through. You can use a bit of masking or painter’s tape to hold them in place. Use the included Allen wrench to tighten the set screws, which lifts the packet, and pins the hammer and trigger pins into position.

Timney is careful to explain that if you have a polymer material lower, you should put a thin aluminum plate underneath the trigger as a bearing surface for the screws. Otherwise, they will gouge the receiver and fail to lock into place.

Note the two securing setscrews on the bottom of the Timney housing.

Me, I’d add another step. Once the Timney is secured, and you’ve test fired it enough to know that it works, degrease the interior and apply dabs of paint to lock the set screws in place. You don’t want to use wicking Loctite, because you might want to remove the packet at some future date. Paint will lock the screws and indicate if any break loose.

FINAL TRIGGER FUNCTION CHECK

After swapping, tuning and adjusting your parts, must make sure they work properly. Here’s the process. Make sure the rifle is unloaded, and that no loaded magazines or loose ammo are anywhere nearby.

Close the bolt, turning the safety on. Depress the trigger, putting at least 10 pounds into it. Let go of the trigger, and then turn the selector to Fire. If the hammer drops, you’ve got problems. If the hammer doesn’t fall, proceed.

Dry fire the rifle, holding the trigger to the rear. Work the charging handle to cycle the bolt. Pull the charging handle back, then ride it forward. Yes, you are not supposed to be riding the handle, usually, but we’re checking one thing at a time here. Slowly ease the trigger forward. You should hear and feel a click when the disconnector hands the hammer off to the trigger nose. If there is a loud “clack” sound as the hammer falls on the firing pin, you have a problem. If normal, proceed.

Dry fire again. When you hold the trigger back, yank the charging handle back hard and let go, in one motion. Ease the trigger forward. No click? Good.

Put the safety on and lock the bolt back. Use the hold-open button, and release the bolt so it crashes home with full force. Turn the selector to Fire, and dry fire again. The trigger pull should be normal.

Now for the potentially abusive part. Leave the selector on Fire. Lock the bolt back, then push the button and let it crash home. Dry fire. If the trigger pull is normal, you are done with dry testing.

If at any time during this process the trigger pull changes, or the hammer falls when you don’t intend it to, you have erred in trigger pull tuning and need to go back and do it again.

PROBLEMS?

If you do the function check and find your rifle doesn’t work properly, you have to dive in and see why. For this, the Brownells Dryfire Jig is very, very useful. It allows you to mount the parts on the exterior of the lower you will use. That way, if there is some anomaly in your receiver that is causing the problem, you can see it.

The jig is easy to use. Employ the long pins to hold the jig on the side of the receiver. Place the parts in the jig, in effect assembling them outside of the lower. Then watch while you re-create the problem that happened during the function test.

HAMMER DROP ON SAFETY

You can experience a hammer drop either with the safety on when you press the trigger, or when you press, release and rotate the safety. The problem is usually the trigger. It can be caused when the trigger is too short on the back end, with too much clearance between it and the safety (there should be none when the selector is set on Safe). It can also happen when the trigger pin hole is in the wrong place.

If it's a trigger pin hole issue, you have no options. Send the lower back for replacement. You haven’t done anything to it, have you?

If the problem is the trigger, you can swap out the offending one for another with the proper dimensions on the rear. Failing that, you can use a high-temp silver solder to fabricate a thin piece of steel on the backend top of the trigger. File the solder until it is only tall enough to block trigger movement, but not so tall it keeps the safety form being turned to Safe.

This happened on rare occasions back in the early days. Today it is unheard of. The last time I mentioned it in an armorer’s class, the students collectively looked at me like I was describing how to knap flint.

HAMMER DROP ON TRIGGER RELEASE

This is easy, it is an early disconnector, which we’ve discussed before. Simply time the disconnector correctly.

HAMMER DROP ON BOLT CLOSING

This is due to minimal sear engagement, or a trigger spring that is too light. If the sear engagement is minimal, this is a geometric problem caused by the hammer, the trigger or the receiver pin holes. Whichever it is, replace.

It is possible that the trigger spring is too light. If you think that is the case, replace it with a new full power, USGI spring and test again. If it still happens, then the problem is geometry, not spring tension.

CHAPTER 8
LEADE AND AMMO

The travels of a bullet are impressive. That it works at all is a testament to the ingenuity of inventors across the centuries. The bullet is all cozy in the case, resting in the chamber. Then the firing pin strikes the primer and all hell breaks loose. The powder begins to ignite, but the building pressure pushes any remaining unburned powder forward before all of it can be consumed. Case neck tension and the crimp try to keep the bullet in place but the pressure builds too quickly for them to do much more than increase the efficiency of the reaction. The bullet moves before the powder has all burned.

This is not the situation in some handgun cartridges, in which all of the powder has been consumed before the bullet can fully exit the case — sometimes before the bullet has begun to move. In rifles, there’s a lot of powder stacked away from the primer.

The only tool (besides Cerrosafe, or a casting) to tell if you have a .223 or 5.56 leade, is the 223/556 Gauge from M-guns.

The rifle bullet, broken loose by the pressure of expanding gas, begins moving forward. It accelerates until it strikes the leading edge of the rifling. It is this short section which is called the leade, or freebore. The bullet rests in the chamber just forward of where the case neck stops. It is here that there is a tiny shoulder or ledge, behind which is enough room for the case neck, forward of it just enough room for the bullet. (This is why you need to trim your brass when reloading, because it stretches on each firing. If you let it stretch long enough, the front of the neck will bump up against this shoulder, in effect crimping the bullet, resulting in spiked pressures upon firing.)

The section forward of the case neck allows the bullet to move, but not create so much room that the bullet will tip or wobble as it travels forward. The diameter of this section is very important. And the length between the bullet’s starting point and the beginning of the rifling is also critical.

You see, when the bullet engages the rifling, it slows down. It must, requiring energy and time to engrave the rifling into the bullet jacket. The burning powder is still expanding and, when the bullet slows down, pressure increases. (This is an unavoidable result of the ideal Gas Law.) Every rifle cartridge has a carefully designed distance for the bullet to travel, so the pressure generated is enough to deliver velocity but not so much to create a pressure spike and excess stress for the design.

This is the result of using the reamer from Ned Christiansen. A clean, 5.56-length leade that will control pressure spikes in your rifle.

Once the bullet has been fully engraved along the full length of its bearing surface, then the force required to move it is less and the spike drops.

Pressure is not a simple thing. And it is not a singular thing. Any batch of ammunition will have varying pressure and velocity. We accept that a batch of ammo has a high and low velocity, an average, and an accepted spread or deviation. So it is with pressure. And each cartridge has a defined maximum pressure and maximum allowed average pressure. Manufacturers stay within those limits.

To add to the confusion, how you measure pressure also matters. The old system was called (for rifles) the “copper-crusher” method. A small cylinder of copper was placed in a fixture where the chamber pressure of the cartridge could act on it. The test lab would fire the round, the copper cylinder would be hammered by the pressure and squashed a small amount.

From top to bottom, the lengths of the leades in 223, 5.56, and 5.56 reamed with the Ned tool.

The lab would then compare how much the cylinder was shortened with a comparison table, inferring the chamber pressure created. Lower pressures of shotguns couldn’t squash copper, so they used lead, and that is what you see in old texts on pressure — CUP and LUP, copper units of pressure and lead units of pressure, respectively. They were somewhat carelessly referred to as PSI, pounds per square inch.

The leade is subject to wear from use. This bore has pits and the leade has eroded forward.

Modern labs use piezoelectric sensors. A “piezo” is a crystal that has a known conductivity to electricity. That conductivity changes under pressure. If you compress a piezo you can get a direct readout of pressure. (Once you know the compression-to-conductivity ratio, at least.)

The CUP system simply told us the total work performed on the cylinder. The piezo system tells us (if you have one with a quick enough refresh rate) what is happening at every microsecond of the firing. This led to new information, some of it not all for the good. It turns out that some commonly accepted loads had, hidden in the event, strange spikes of pressure that exceeded the safe pressure ceilings of the cartridge. Some loads had to be altered, and others dropped.

With a gauge, chamber brush and reamer, you can make sure your rifle does not have pressure problems from a .223 leade.

Apply a coating of ink from a Sharpie to see exactly where your gauge is rubbing on the leade.

There is no “conversion value” from CUP to piezo PSI. Each cartridge had to be tested all over again with the new piezo systems.

To make things really complicated, the pressure you register depends in no small part on where you put the piezo monitor. The American 5.56x45, with its pressure maximum of 55,000 PSI, is not necessarily different from the NATO 5.56x45, with its C.I.P-defined maximum of 60,000 PSI. You see, we Americans measure pressure in the middle of the case, and the Europeans measure it at the case mouth.

PREVENTING PRESSURE PROBLEMS

Bullet design and length have a large effect on pressure. A longer bullet, if that length is the full diameter of the bullet/bore, will stall longer in the leade, simply because there is more bullet to engrave. Heavier bullets will cause more of a spike, all other things being equal. But material matters, too. An all-copper bullet is harder, therefore taking more work to engrave. The all-copper tactical, heavyweights and tracer bullets, have to be loaded to a different recipe in order to control the pressure spike. It also follows that they will have a higher pressure increase if they are fired in a chamber with a .223 leade instead of a 5.56 leade.

I keep pointing this out because it matters. Rifles can stop working due to pressure problems left uncorrected.

Lastly, the spread, known as standard deviation, or SD is a consideration. SD is a statistical measurement of group variability. A bigger SD means you have rare events that are further from the average than a set with a small SD. When the manufacturers, or loading books, consider the maximum pressure average they will accept, they have calculated the SD and how high the highest round will be in pressure. Just because your 5.56 ammo has a book value of 55,000 PSI as the max, some loadings may only generate 52,000. Or 48,000, on average, because the SD is large enough to keep the outliers under the 55,000 PSI ceiling.

Some bullet/powder combinations will have lower SDs than others, thus can crowd closer to the max.

And they do this knowing the chamber dimensions for that cartridge.

.223 REMINGTON VS. 5.56X45

The .223 Remington and 5.56x45 are not the same. The 5.56 has a longer leade, a longer distance between the bullet start and the onset of the rifling. The rifle and cartridge designers did that deliberately to allow for a hotter load and higher velocities because the longer leade allows for more run-up to the engraving.

Some 5.56 chamber drawings show a larger leade proper diameter than the .223. This larger diameter is there less for pressure than function. In a really harsh environment, a skosh more room in the leade can keep a rifle running, where one with a tight leade (not a short leade, the two differ) would choke. The government is more interested in a rifle that keeps working, even if it means they have to accept a 3 MOA accuracy level, instead of a 2 MOA potential.

When you put 5.56x45 ammunition, meant to utilize a longer leade, into a chamber cut for the .223 with its shorter leade, you get a pressure spike. How much? To find out, I sent some 5.56 ammo off to a test lab. No big secret, the ammo was a batch of Federal XM-193, 55 grain FMJ brown box. I had them test it for pressure in two laboratory barrels — one chambered in 5.56, the other in .223.

Federal understands the difference between .223 and 5.56 leades and marks their boxes appropriately. In fact, all the ammo companies do. Don’t think they randomly label their products, they don’t.

In the 5.56 test barrel, the XM-193 produced 48,000 PSI. A little on the low side, but since it delivered the expected velocity, why should Federal have loaded it any hotter? In the .223 barrel, the same ammo produced 62,000 PSI. That’s a big spike. Now, someone is going to say that is no big deal. They’ll assert your AR can shrug off a diet of 62,000 PSI ammo, after all, it isn’t that much more than the 55,000 PSI the spec calls for, and hardly anything over the NATO pressure.

By reaming with the Ned Christiansen tool, you’ll only be removing metal form the leade, not the shoulder.

Remember my advice about people you can ignore? This is one example. A pressure increase of 29 percent is not “nothing.” And what if the original pressure had not been 48,000, but something more like what we’d expect, say 52,000? Then a straight 29 percent increase (and this is not usually a linear response) would make it 67,000 PSI. I have talked to other gunsmiths and AR-savvy people who have done the same thing and their experience of a 52,000 original round has been more along the lines of 72,000 PSI.

A .223 leade means a “popped” primer. In this case, the primer ended up in the locking lug recess and kept the rifle from firing. Don’t blame S&W, this is not their upper on that lower.

A 29 percent increase is pretty close to the increase in pressure that a proof round produces.

How do you know if your barrel is .223 or 5.56? Measure it with a gage produced by Ned Christiansen. If you have a .223 instead of the 5.56 you thought you had, ream it with a 5.56 reamer from Ned.

The gage has a short section that replicates the neck and leade of a 5.56 chamber drawing. You drop the gage into a recently cleaned chamber. If the leade has been cut to .223 dimensions, it wedges in place. However, if by turning the receiver upside down, the gage falls out, you have a 5.56 leade. If it wedges in place, you have a .223 leade.

Use a felt-tip marker to darken the gage to see exactly where it is binding. But while that can be fun, it does not correct a short leade.

And a reminder, this has nothing to do with headspace.

The reamer is designed so that it will cut the leade, and only the leade. It is meant for carbon steel, stainless steel and chrome-plated bores. It will not cut a barrel treated via the Melonite process, and attempting that will only dull the reamer. You can spend all day using it in the appropriate barrels, and not change the headspace at all. The process goes like this. Having cleaned the chamber, apply a bit of lube to the cutting flutes of the reamer. Insert the reamer and turn clockwise as it bottoms out. You’ll feel it cutting. Once you feel that it is no longer cutting, keep on rotating it in the correct direction as you pull it out.

An erosion gauge is not supposed to fall this far into the bore when used as a test. Note the butt end of the gauge in the receiver. It should be 6 or 8 inches outside of the receiver.

Do not rotate backwards. Do not simply drop it in. Keep rotating clockwise as you lift it out.

Brush the chips off the reamer, and put it away. Swab the chamber, then push a patch down the bore to get all the chips and cutting oil out of the bore. Done.

REMEDIES DISCARDED

If you don’t correct the leade, expect increased pressure from each and every round to loosen primer pockets. Some primers will abandon their assigned posts before they exit the receiver. Those loose primers will rattle around inside the receiver until they can cause some mischief. In classes, we’ve seen them wedge under triggers, against disconnectors, under safeties, in between moving parts, even drift up into the charging handle slots, the gas key and locking lug recesses.

We’ve even seen an instance of an expended, popped-out primer falling onto the magazine, interfering with the next round coming up, causing the rifle to close on an empty chamber.

This was one of the weirdest malfunctions I’ve ever seen. The popped primer dropped in the magazine, causing a failure to feed.

These are all bad. While I have to laud DPMS for coming up with the receiver rug many years ago, the real answer is not a rug, but a proper leade.

FACTORY AMMO

If you reload, you know that “X grains of Blast-em Powder, under a 55-grain FMJ, loaded to magazine length, produces 3,100 fps.” The factories do not load that way. The powder you use to load is called “canister grade.” Powder is made in batches and, while each batch is a precise recipe, the results are not identical. Let’s call the burn rate of Blast-em Powder as 100 on the burn scale.

Ammo companies know what they make, and they mark it accordingly. This is 5.56 ammo, and you should not be using it in a rifle with a .223 leade.

Our fictitious powder has a production acceptance rate of 96 to 104 percent burn rate. The batch will be made, dried, cured and tested. If the burn rate is within 96-104 percent, it passes and is added to inventory as arsenal-grade powder. If the company sells the powder to an ammo maker, they ship it along with the test info. The ammo company then takes “Blast-em, burn rate 98.3 percent,”(or whatever it was, according to the spec sheet) and loads their ammo.

Each production run will use only one batch of powder, one batch of primers, one batch of cases and one batch of bullets. That run is given a unique lot number. If anything has to be changed, those subsequent rounds are a different lot number.

The allowable headspace on an M249 is much more than on an M16. Reloaded brass that originally went through an M249 can have a very short life in your rifle. DoD photo by Lt. Col. Daniel Bohmer, U.S. Army.

When the powder company makes canister grade stuff they mix equal amounts of 97 percent and 103 percent to make 100 Blast-em (as an example).

So, if you break down factory ammo, sometimes the powder charge will have a given weight and sometimes it will be more or less. That’s because they used different lots of arsenal powder, not canister-grade.

You are told not to mix powders, so why can the powder makers do it? Simple: their powders have consistent grain size and density. Once mixed, they will not settle out. Dissimilar powders will settle out, and you will make a mess of things. Don’t do what they do.

PRESSURE CONSIDERATIONS

Just what kinds of pressures are we talking about? There’s no quick answer, so I’ll provide a sparse response to get the concept across. The pressure limits of the ammunition we’re talking about are:

.223 Remington | 55,000 PSI
M-193 5.56x45 | 55,000 PSI
Mk 262 Mod 1 | 58,000 PSI
M855 | 58,000 PSI
M855A1 | 64,000 PSI

Before you go and splash those numbers all over the Internet, keep a few things in mind. Those are the maximum allowable pressures. The maximum average pressure of any given load will be lower. As pointed out earlier, one XM-193 lot I had tested produced a pressure fully 7,000 PSI under the maximum allowed.

Remember, too, that the .223 is measured in a .223 chamber with a short leade, and the others are measured in a 5.56 chamber with a longer leade.

These are piezo-measured pressures, and not to be confused with the old copper-crusher figures, published in older data. So, if you see a reloading article or manual written before the piezo era with powder weights appreciably higher than what you see today, don’t use them. Use modern data. And keep in mind that every time you touch off a round, the mechanism you are holding was designed to contain these pressures, not higher. There is no such thing as a free lunch. At every gun club I’ve ever been to, there’s one guy who claims the ammo companies are somehow conspiring to cheat us all out of the feet per second we deserve. Do not believe him, do not use his loading data and do not shoot his ammo in your AR.

The DPMS receiver rug is a stopgap solution to blown and popped primers. Better to ream the leade, but if you can’t, install this instead.

And please note that higher pressures found in some tactical ammo are there as a calculated trade-off. The government is willing, in some instances, to trade a small amount of service life for a small, but sometimes noticeable increase in performance. If you want that performance, you have to be willing to trade off service life, too.

If it is newer than M855 (the mid-1980s) and it is military, you can be sure it is 5.56 and should be treated accordingly.

LEADE CHANGES

As you shoot, the impact of the bullet on the rifling and torrent of hot gases and powder granules wash over the leade. This erodes the beginning of the rifling. The military uses an erosion gauge to measure the service life of a barrel. Once the leade has been eroded far enough, it is considered used-up, and is replaced.

The amount of forward movement of the leade that is tolerated can be short, relatively speaking. Burn up an inch of the rifling, and the bore is considered shot-out. Leades erode and do not last forever. But you can’t expect a .223 leade to erode to 5.56 length, and solve your problem.

DPMS RECEIVER RUG

There are some end users who cannot ream the leade. Their department won’t allow it. Or it is a tool that is forbidden for use. In that case, a DPMS receiver rug can be a temporary solution. It slips into the lower receiver under the trigger (you have to remove all the internals to install it) and blocks any popped primers from getting under the trigger. It isn’t perfect, but it is better than nothing.

PRIMER FREE-FOR-ALL

Excessive pressure loosens primer pockets and they fly everywhere. We’ve seen them in all areas of receivers, the bolt, the charging handle, even causing mayhem in magazines. The really troublesome ones fall into the barrel extension. Not because they cause any more trouble than other places, but getting the crushed primer out of there can be a real headache.

.223 leades are a real problem, and those who say otherwise are kidding themselves.

CHAPTER 9
HANDGUARDS

When medieval hand cannons became actual weapons, and it was possible to shoot them quickly enough to heat them up, it became necessary to add some kind of hand protection out on the barrel. In the old days that meant wood, but on today's AR, it's plastic handguards, usually with metal heat shields inside to keep the heat at bay. This works pretty well, actually. However, in really hard use or in hot, sunny climes, it can be a bit much. That’s why all the cool, bearded guys wear gloves.

The heat shields protect your hands by reflecting the heat back to the barrel, preventing escape. The USGI handguards comprise three parts, or assemblies — front cap, handguards and the delta/slip-ring assembly.

The barrel nut must be precisely aligned or the gas tube won’t pass through easily, if at all.

The front cap simply keeps the front ends of the handguards in place, with a hole through which the gas tube passes. On the originals, it was triangular, as were the handguards themselves. The XM177 and its descendants had a plain, circular cap with tabs to keep the handguards from rotating. The A2 (yes, there is an A2 front cap) does triple-duty. First, it holds in the round handguards. Tabs keep them from twisting and have two notches cut into the bottom to provide clearance for the M203 grenade launcher. The circular boss on the front of the A2 handguards is notched, allowing it to fit onto the triangular front caps of an A1 rifle.

Yes, you can fit A2 handguards on an old A1, or SP1 and even many others.

The original handguards were paired, right and left, and were triangular. They work pretty well but the plastic of which they are made is quite fragile, and you rarely see them without some damage from use.

The XM177 handguards were circular. The earliest ones lacked any heat shield. Later versions have a single panel in each half. Like the A2 handguards that were patterned from them, they are not paired. They fit up and down and are identical, so you don’t need paired spares.

The “C” clip on the back of the delta assembly is best dealt with by means of reverse pliers. Anything else, and you risk hurting yourself.

The A2 rifle and CAR handguards sport a single plate, but those on the M4, which are oval and much taller, have two plates for better heat control. The delta ring, or slip ring, is the spring-loaded assembly that traps the rear lip of the handguards. You must press this assembly out of the way in order to take the handguards off.

The A1 handguard (in front) is comprised of left-and-right pairs, while the A2 (behind) is symmetric and can be used either on top or the bottom.

To take the delta ring apart, remove it and the barrel from the upper receiver. There’s a “C” clip in the back, requiring a pair of reverse pliers for expansion and removal. Expand the “C” clip, pull it away from the barrel nut, and the spring coil comes free. Pull the spring coil and the delta ring off the back of the barrel nut. This reveals a bare barrel nut onto which you can install your free-float handguard.

All of this is well and good, and the only choice if you are doing a retro build. But, if you expect to mount a light, laser or other extras on your rifle, you will find the standard handguards lacking. What can I say, back in the 1960s, 70s and 80s, no one was thinking about lights and lasers.

SIMPLE HANDGUARD PROCESS

Before you go and tear your rifle apart and hammer your credit card for an expensive free-float handguard, here’s a simple way to get rails without a lot of work. Many companies make replacement handguards, ones with rails that simply take the place of your USGI ones.

The swap is simple; remove the old, install the new ones in their place. Done.

RISE OF THE QUAD-RAIL

One aspect of the modern military toolkit is the targeting laser designator. Projecting an infrared laser, which can be seen with night-vision optics, it pinpoints where the dot is aimed. Pilots, incoming bombs and artillery shells can all see it. This is old hat, but how is such a beast aimed?

Rails that extend all the way out to the muzzle allow you to mount extra gear, like this thermal sight from Insight.

As a hand-held unit, it is unsteady. Bolted to a rifle it is a lot steadier and doesn’t have to be pulled out of a pocket or web gear pouch to use.

Long story short, the military adopted a rail-on-a-rifle as the place to mount it. And since the handguards had to be replaced to do this, why not make the handguard railed on all four sides? Thus the quad rail was born.

One of the virtues of the quad rail is that it permits bolting on extra gear, like this AN/PEQ2A. Then again, it lets you bolt on more stuff than you’ll want to carry, too. Show some restraint.

However, the quad rail has since been replaced, discarded and made obsolete. It is bulky, heavy and sharp-edged. It had standard Mil-Std 1913, aka Picatinny rails. But we’ve grown up since then and have rediscovered the idea that a rifle or carbine should be handy, and not a place to bolt all sorts of handy tools.

Today, we have returned to slimmer free-float handguards. But unlike the earlier ones, which were simple tubes of aluminum or carbon fiber, these still have places to which you can attach accessories. They are just much, much sleeker.

The 1913 rail has been adopted by NATO as the Stanag 4694. Its slot locations and rail dimensions are precisely defined. But experimenters have gone much beyond that. The two current competing designs, both of which were released to the public domain, are Keymod and M-Lok.

The Keymod and M-Lok do not have rails, but slots. To attach something to a 1913 rail, you had to have the device (light, laser, cup holder, whatever) and you needed a rail-grabbing clamp in between. The Keymod and M-Lok attachment systems, on the other hand, involve clamping into slots. The clamping system can be built directly into the light, laser, etc. These systems are lighter, less bulky and less expensive than a Pic rail lash-up.

The delta ring assembly removed from the barrel nut. Left to right; the “C” clip, the spring coil, and the delta ring itself.

Keymod and M-Lok compete. They are not cross-compatible. So the specific slots are machined directly into the handguard. Pick one design or the other and your accessories will need to match whichever you choose.

MODES OF ATTACHMENT

Replacement handguards fall into one of four different camps.

Simple swaps

Clamp on the barrel nut

Clamp on the barrel nut, the sight has to come off

Replace the barrel nut

Simple swaps are just that. Wrestle the old handguards off (there’s a reason the service manuals show four hands involved in the assembly/reassembly of handguards). Replace them with new handguards that have some feature you find more desirable than the old ones.

Handguards of the ‘clamp on the barrel nut’ variety do just that. Some can be a struggle to install with the fully assembled delta or slip ring still in place. However, most require removal of the ring assembly. The less involved way is to fire up a cutter of some kind and simply hack off the delta/slip ring, spring and e-clip. This way you don’t have to remove the front sight assembly, spin off the barrel nut, remove the offending parts and reassemble the barrel into the upper.

Of course, a handguard that clamps onto the barrel nut, but does not require sight removal, has to be a two-piece unit. It also has to play well with the front handguard retainer. That leads us to our third type.

The clamp-on handguard is one single tube. Yank the barrel assembly off of the upper receiver. Remove the front sight. Grab your reverse pliers and remove the e-clip from the barrel nut and strip those parts off. You can replace the original front sight or install a replacement gas block. That depends on the handguard and your preferences.

If you want rails, Blackhawk has a solution.

Last up is the type of handguard that replaces the original barrel nut. It can be a proprietary nut to which the new handguard attaches. Or, you can get a one piece nut and handguard. The former is commonly found on the old quad-rail and the new Keymod and M-Lok handguards. The latter is common on the plain old aluminum tube handguard, which was all the rage back when Reagan was handing off the baton to Bush the elder.

The best way to deal with free-float handguards is to strip the receiver down to the upper and the barrel. Or build from new parts.

Each system has its own specific tools and tips on how to save your fingers from blood blisters, barked knuckles and parts mismatches.

The free float handguard is a great place to mount a light, for use at night and whenever the power goes out.

HANDGUARD LENGTH

If you are going to keep the existing front sight tower on your barrel (you’ll probably have to take it off, and then re-install it, depending on handguard design) you’ll want a handguard with a length that does not extend past the rear of the front sight tower. If you’re using a low-profile gas block, run the rail past the block. The typical low-profile gas block is held in place by means of a pair of set screws. While it isn’t exactly fragile, it can be bumped out of alignment. So you want the rail to cover it. You can even get a rail larger and wider than a suppressor, and longer than the barrel, so the suppressor is inside the handguard.

The Brownells rail alignment tool aligns the handguard perfectly with the receiver rail.

A carbine handguard must be no longer than 7 inches to fit behind the front sight. A mid-length gas system calls for a 9-inch handguard, while a full length rifle needs an 11-incher. To cover a low profile gas block, add 2 inches to each of those lengths.

FREE-FLOAT PREP AND TOOLS

To install a free-float handguard, remove the regular front sight assembly. The best ones have two tapered pins holding the sight assembly onto the barrel. Do yourself a favor and order the sight block from Brownells. It holds the sight, provides a support on which you can hammer, and tells you clearly which side is which.

Start with a punch that's tapered, which will reduce the chance of bending or breaking. If a proprietary barrel nut wrench is provided by the manufacturer, use it. However, a strap wrench can often be an even better tool. A strap wrench employs a band of tough rubber as the gripping surface. Wrap the strap around the part, pulling it tight. Correctly installed, the wrench self-tightens as you lever. You don’t need a firearm-specific wrench, these are thick as thieves at the local hardware store.

LARUE

LaRue was the company that sold truckloads of classic quad rails to the DoD. These required a good bit of fitting as the railed handguard is made of five parts — handguard rail, barrel nut, spacer, nut and keeper — plus a couple of bolts. And it takes some creative juggling to install.

Start with a barrel in a receiver, or strip off everything from an assembled rifle. Things to remove include flash hider, front sight housing/gas block, handguards, delta ring assembly and barrel nut. Take the keeper, the half-moon shaped piece, and hold it against the front face of the receiver. Slide the handguard nut on and spin the new barrel nut onto the barrel. Torque up the barrel nut just like you would any other, as described in the barrel chapter.

Place the spacer in the rear of the handguard. Slide the handguard onto the barreled receiver. Hand turn the handguard nut, catching the threads on the handguard itself and rotate until you have pulled everything up to the receiver. As you tighten, you’ll have to jiggle things a bit to get the locating pins to align.

The LaRue free-float handguard uses a steel anti-tilt plate to resist rotation of the handguard in use.

LaRue not only uses an incredibly strong locking nut to hold the handguard together, but builds in QD sling swivel sockets.

The LaRue handguard is free-float, and sturdy enough to use as a bridge support if you ever have to hold something up.

Hand tighten the handguard nut and keeper, while observing spacer alignment. A tight handguard nut is the key.

With the handguard nut hand tight, line up the keeper and spacer, jostling the locking bolts, finger turning them until they catch and align. Take a moment to check alignment of the top rail of the handguard with the top of the receiver rail. They must be in agreement. Once everything is lined up, use a strap wrench to fully tighten the handguard nut. Then tighten the locating bolts in the keeper, using the supplied blue Loctite. Torque to 25-30 in. lbs.

Once the LaRue is installed, go back (or, if building up, proceed) to install the gas block or front sight, the gas tube, flash hider or muzzle device and the rest of the rifle.

A few pointers. For a clamshell receiver holder, you might have to dremel clearance for the keeper in the face of the blocks. If you are wedded to barrel blocks, you’ll be clamping, un-clamping and clamping again to hold things while you remove and install the various parts. If you use a reaction rod, the receiver will try to slide back from the handguard parts as you work with them. Keep an eye on the receiver, or it may slip back and cause minor headaches.

This is the classic, the quad rail of all quad rails. It will be bulky. You may be tempted to put rail ladders on it, to protect your hands from the edges. If you do, it will get even bigger. But you will be on your way to making an M4 clone, suitable for deployment to dusty places.

MANTICORE ARMS

The first thing to know about the Manticore Arms Transformer rail is that it can be whatever you want it to be. Unlike others, where you have to pick one and stick with it, the Transformer can be all things to all people. The handguard itself is just the frame, onto which you attach the panels — Keymod, M-Lok, or non-attachment style in snakeskin or “frag” patterns. I’d bet, if you were just a bit clever, you could modify one of those to be a mil-std 1913 panel, and have everything.

The Transformer uses a proprietary barrel nut, but here the inventor got clever. Instead of a profusion of notches requiring alignment with the gas tube, the barrel nut has a colander’s worth of screw holes to line up the top rail on the handguard, with the rail on your receiver. The gas tube rides over the barrel nut, not through it.

Start with a receiver and barrel. Slide the barrel nut on, with the smooth (unnotched) end toward the receiver and spin it into place. Use the provided barrel nut wrench to tighten the nut. Follow the usual process, tighten up three times. Manticore suggests you tighten the nut until the top row of screw holes is perfectly in line with the gas tube. That’s a bit too uncertain for me.

Manticore, with the multiplicity of bolting screw holes for the forearm. It’s easy to align and simple to bolt on.

Slide the handguard on. Line up the attachment screw holes in the handguard with those in the barrel nut. Check alignment of the handguard rail (there are two sections, one at the rear for scope mounts, the other at the front for sights) and the receiver. Hand tighten an attachment screw or two to keep things in place while you use a straightedge to check. Adjust the barrel nut back and forth until the alignment is perfect.

Once the alignment is good, take the handguard off and install your gas tube or piston system. It is easier to do it now than after you have bolted the handguard in place.

Slide the handguard on, line up the screw holes and bolt it down with 25-30 in. lbs. of torque.

A few tips. Since the barrel nut is not locked in by the gas tube, use a dab of blue Loctite. If you’ve applied more than the minimum 30 ft. lbs. of torque, it isn’t going to come loose in use. This is your call. I definitely use blue Loctite on the screws holding the handguard to the barrel nut. They will be subjected to a lot of vibration and heat and don’t have a whole lot of thread surface holding them in place.

The Manticore Arms handguard offers you any system you want; Keymod, M-Lok, non-slip no-lock.

To attach the flat-style panels, use round head screws. For Keymod or M-Lok panels, flat head screws. If you use the round head screws on the Keymod or M-Lok panels, the heads will interfere with the installation of your accessories. Save the barrel nut wrench (even write on it what it is for) in your toolbox. If you ever want to take the transformer off, you’ll need it.

GEISSELE SUPER MODULAR RAIL

The Mk8 M-Lok rail is for the M-Lok system of attachments. Slide the Geissele barrel nut onto the barrel and hand tighten. Use the Geissele barrel nut wrench to torque it to 40 ft. lbs.

Note that the Geissele nut does not have the flange and teeth of a standard nut. That’s because it doesn’t need to be indexed for clearance of the gas tube. What keeps it from loosening is 40 ft. lbs. of torque. In addition, the handguard is a tight fit on the nut. And the clamping bolts that hold the handguard in place not only squeeze it onto the nut, but also pass through grooves in the nut, adding gripping force.

With the nut tight, wipe a thin film of oil onto the outside of the barrel nut, and slide the handguard on. The fit is machined to be tight, but it shouldn’t bind or require force. If the handguard won’t go, stop and inspect. The edge of the barrel nut might have become dinged, creating a troublesome little burr. Do not force, find the source of the issue.

Geissele M-Lok Super Mod, showing the orientation of the barrel nut, clamping screws and forearm.

The dogbone, the part into which the threads screw. Steel threads on a steel clamping plate like this are incredibly strong.

Slide the handguard onto the barrel nut, pressing it against the receiver. Pass the two mounting bolts through. Wiggle the handguard to align the bolts with the grooves so they pass through. Once through, hand tighten the bolts to the dogbone-shaped anchor plate on the other side.

Don’t fully tighten. You need to precisely align the top rail of the handguard with the rail on the receiver. You can do this with the Brownells alignment clamp, or you can attach a scope mount across the gap (rear on receiver, front on handguard) and tighten, forcing the two into alignment.

Once aligned, torque the bolts to just 5 ft. lbs. with a short Allen wrench. Examine the pair of ⁵⁄₆₄-inch Allen set screws on the rear of the handguard. Use the supplied wrench to tighten them against the receiver.

That’s it. Remember, Geissele specifies that the main bolts do not exceed 5 ft. lbs. of torque. Since 5 ft. lbs. is equal to 60 in. lbs., that's actually twice the torque to which you tighten your scope mount screws. If you are worried, then use a paint pen to mark the ends of the bolts where they come through the anchor plate.

As with other handguards of this type, it is a whole lot easier to install the gas tube and block — or piston system — before you slide the handguard on and bolt it down.

ALG DEFENSE

The ALG Defense V2 is an M-Lok type handguard. The V2 comes with shims to correctly time and torque the barrel nut. To install, lightly oil the threads and slide on the black shim from the pack provided. Screw the barrel nut on, tightening three times with the supplied wrench. Inspect the timing of the nut with the black shim in place. The timing of the nut, indicated by the markings on the provided wrench, will tell you which shim (or shims) you’ll need for correct timing. This is needed because the V2 is like the standard barrel nut in that there are only certain timing locations that will permit the gas tube to pass. Unlike a regular barrel nut, with a large number of notches, the V2 only has eight.

With the V2, you don’t need a torque wrench because the dimensions of the nut, coupled with the properly selected shim, will generate the correct torque on the barrel nut.

Once the barrel nut is tightened and aligned, install the gas or piston system.

The ALG Defense proprietary barrel nut doubles as its own timing gauge.

Like the Geissele, the V2 handguard is machined to be a snug fit over the barrel nut. If it won’t go, don’t force it. Find out why, and correct it. A burr on the leading edge or some grit stuck inside the tube can cause a problem. A little oil on the barrel nut won’t hurt.

The handguard has two small tabs on the rear; these are meant to nestle on either side of the upper receiver. They are an anti-tilt measure, along with the gas tube. When you fit the handguard in place, the screw holes in the barrel nut must line up. If they don’t, you’ll have to tweak things to get everything to align before you can tighten the handguard screws.

With the nut tight, use the wrench to calculate the shims you’ll need. Then, once the shims are in, the wrench shows you the correct torque.

Use the short-arm Allen wrench to tighten the handguard screws. Once tight, and you have test fired and made sure everything is correct, paint them in.

Here’s a pro tip. The V2 handguard comes with five shims, of which you may only need one or two. Maybe none. Save them and the instructions to fit barrel nuts onto other builds later on. Or, if you want to re-build, and use the V2 on a different upper, you may need them for that project.

With the barrel nut correctly torqued, the alignment tabs align as the bolt screws are centered.

BRAVO COMPANY

The BCM KMR is a Keymod handguard, requiring that type of attachment system.

To install, apply a light coat of oil to the receiver threads and spin the barrel nut into place. Use the BCM wrench and tighten the nut four times, to 40-50 ft. lbs.

Install your gas tube and block, or the piston system.

Take the BCM index plate (rectangular one) and slide it onto the upper receiver with the tabs toward the rear. Slide the handguard on. It is meant to be a tight fit. If you can’t get it to fit, use a hair dryer to heat the back end of the handguard. The heat will expand the inner diameter, allowing it to slide on easier. Don’t overdo this; aluminum conducts heat really well and you can make the handguard too hot to handle if you aren’t careful. If you have to use more than hand pressure, light taps with a rawhide or rubber mallet will work. Trap the index plate between the handguard and the upper while aligning them.

The handguard does not quite get snugged all the way against the receiver. The locking bolts have to pass through the trough in the barrel nut, and this alignment is more important than having the handguard tight to the receiver. Adjust the handguard until both cross bolts will pass through.

Press a cross bolt through a clamp block and insert in the handguard. Repeat from the other side. Tighten the two bolts only until they will hold the clamp blocks in place. Notice that one of them has notches, and the other doesn’t. Tighten the notched bolt until it is up to at least 30 in. lbs. and one of the notches aligns with the threaded hole in the clamp plate.

The BCM handguard uses a separate locating tab, requiring alignment as you slide the handguard into place.

Tighten the other one up to 30-40 in. lbs., no more. The end of the second bolt passes through the notch in the other bolt, locking it in place.

The beauty of this system is the multiple interlocking parts that resist loosening and rotation. The index plate keeps the handguard from tipping, while the cross bolts, prevent the barrel nut from turning. One bolt has to loosen and practically fall out before the other can turn at all.

Light in weight, strong, and locked to the receiver, the BCM KMR is an excellent handguard.

The notched nut is screwed in first, the other locks it in place, sliding through one of the gaps.

DANIEL DEFENSE SLIM RAIL

The Daniel Defense SLiM Rail uses not only its own barrel nut, but a clamping system that is massively over-engineered. To install, slide the bolt-up plate onto the barrel, back to the receiver. Make sure the alignment tabs ride around the upper, and that the gas tube clearance hole is in line with the gas tube hole.

Now spin on the barrel nut, wrench notches toward the muzzle. Use the included wrench (part of the kit) to tighten the barrel nut to 50 ft. lbs. Do not panic if the bolt-up plate is still loose at this point, it is supposed to be. Worry if it is tight, that usually indicates you’ve got something trapped in between the parts.

The Daniel Defense SLiM rail, with the stronger-than-a-bridge clamping system. Here, the alignment tabs are slipped over the receiver.

If you have a low-profile gas or piston system, install it now. If you’re reusing the mil-spec A-pillar sight, it goes on later.

Slide the rail on, using the four bolts to secure it to the bolt-up plate. The screws go in from the buttstock side. Use a gauge or a straightedge to get the handguard aligned with the receiver rail. Tighten the four screws to 32 in. lbs. Paint them in.

The barrel nut is trapped between the bolt-up plate and the handguard, and the locating tabs on the bolt-up plate prevent rotation, plus keep the barrel nut from loosening.

With the barrel nut torqued, slide the forearm on, and thread the screws in from behind.

SAMSON EVOLUTION

The Evolution is one of the simpler handguard installs. It uses the standard barrel nut. So, if you are using the Evolution, leave the nut in place. Or, if building from parts, install the nut and get it correctly timed. As a free-float, it requires that the standard front sight A-pillar be removed, or that you have a low-profile gas block already installed.

Place the two halves of the heat block on either side of the barrel nut. The heat blocks should not be in contact with each other; they must clear the gas tube, and they must be laterally symmetric on the barrel nut.

Hold them in place while you slide the handguard over the barrel and onto the heat blocks. They will be a tight fit and you might have to use a rubber mallet. The exterior diameter of the barrel nut is not a closely controlled mil-spec dimension and can be a bit, shall we say, pudgy in that regard. Once the handguard is most of the way on, make sure the locating tabs on the upper section ride smoothly on either side of the upper receiver. A little wiggling at this point is OK, if you have to make it fit, but you should start as aligned as you can.

The clamping shims for the Samson. Install them evenly and leave room for the gas tube (or piston) and the rest is easy.

Apply a dab of blue Loctite, then start the two 8-32 screws in the clamping tab on the bottom of the handguard. Tighten them alternately and evenly until the inside surfaces of the clamping tab make contact. That’s it, you don’t need to tighten further. Paint them in and you’re done.

MIDWEST INDUSTRIES

The Gen3 M-Lok uses a proprietary barrel nut and locking yoke to resist rotation. Starting with barrel and receiver, disassemble the Gen3. Spin the Midwest Industries barrel nut onto your barreled receiver, using the provided wrench to tighten gradually three times, torquing the last time to 40 ft. lbs.

Install your gas system, block, front sight tower or piston system.

Samson makes the Evolution, featuring locating tabs to keep your handguard upright and straight.

Aerosol degrease the barrel nut. Spread the green adhesive on the exterior of the barrel nut. Slide the handguard on, aligning its top rail with that of the receiver. Again, a scope mount, or a Brownells alignment tool works here. Slide the torque plate into the bottom slot and insert the two cap screws, clamping the handguard and plate.

Once aligned, the Samson is easy; tighten the locking screws and turn in the setscrew.

Tighten the cap screws to 55 in. lbs., watching the assembly to make sure it stays in alignment. (If you have a scope mount or Brownells tool clamped on, they will take care of that for you.)

The Midwest Industries Gen3 M-Lok, showing the orientation of the locking yoke and clamping screws.

MEGA MACHINE MKM

The MKM really isn’t a free float handguard, so to speak. It’s actually an upper receiver and handguard combination that are designed to replicate a monolithic upper receiver. The MKM comes as two pieces, and assembles the same as any other. Install the barrel with the Mega barrel nut, using the included wrench, making sure to get correct torque and timing. Install your gas system.

Then, the easy part. The forward flange of the upper receiver is hexagonal. The interior of the handguard is the same geometry. There is no need to worry about alignment, because the two can only go together on the flats. If you have the rail uppermost, everything is aligned. If you don’t, there’s no mystery about it.

Once the barrel nut is torqued, you can slide the forearm on and align it with the yoke.

Install and tighten the provided locking nuts. You’re done.

PRI CARBON FIBER FREE FLOAT

The PRI is light, hell for tough and well worth it despite requiring a bit of juggling to get together. Standard setup: Start with bare barrel stuffed into the upper receiver. Slide the locking ring on first, notches to the rear. Slide the barrel nut on (use the PRI nut, not the original) and spin it in place. Use the studs on a three-stud wrench to tighten the PRI barrel nut, aligning the holes precisely with the gas tube.

The Mega Machine system incorporates the handguard alignment into the upper receiver extension, so you can't get the alignment wrong.

Once aligned and tight, install your gas or piston system.

Here is the Mega Machine handguard/rail system, correctly installed.

Slide the handguard over the barrel and gas system. Note the two studs on the inside rear of the handguard. These are locator studs that will slip into holes in the barrel nut. As you spin the lock ring, it will pull the handguard toward the receiver. Turn the lock ring and keep the handguard aligned as you do so. This takes a bit of coordination, but once you get the feel for it, things go pretty easily.

Once hand tight, use the PRI wrench (that’s what the notches are for on the lock ring) or you can simply weasel a strap wrench onto the nut and wring it tight. Tight is tight (make it as tight as you can, you’ve got lots of thread engagement here) and then paint it in on the bottom of the handguard where it will be out of sight.

The PRI free-float handguard, with the replacement barrel nut and the tube lock ring in place.

You want the notches on the PRI lock ring to be to the rear.

The handguard has locating studs to ensure correct alignment with the receiver rail.

As you spin the locking ring onto the handguard, it pulls the locating studs into the barrel nut. Once hand-tight, use a strap wrench to fully tighten.

SUMMARY

Not all free-float handguards will clear piston systems, you’ll have to dig for that info yourself. Since the handguard and piston makers are constantly improving and modifying their designs, there’s no way to make a cross-check chart that would be up to date.

You will find that installing the gas or piston system is a lot easier before you get the handguard in place.

Once installed, and locked into place, you can install your front sight, light, laser, bipod, sling gear and whatnot.

CHAPTER 10
FLASH HIDERS AND MUZZLE DEVICES

If you were to believe the anti-gunners, a flash hider is such a psychological inducement to evil behavior that it’s a wonder anyone is alive in the factories that make them.

What does a flash hider do and what exactly is flash?

The only real difference between the A1 and the A2 is, the A2 lacks the three bottom slots.

First, disregard the notion that flash is unburnt powder. If you have not combusted all the powder the case contained in its travel through 16 inches of bore, you’re using the wrong powder. In some handgun cartridges, the powder has been fully combusted before the bullet leaves the case. In rifles, the powder has all been burned by the time the bullet is 3 or 4 inches down the bore. Actually, the bright flash we see is incandescence.

The powder burns at a high pressure and temperature. The confined combustion temperature of your average rifle powder is on the order of 3,500 to 3,700 degrees, Fahrenheit. That gas leaves the muzzle in an expanding bubble. At that temperature the gas is incandescent, and the glow happens to be in a part of the spectrum we can see. Also, the uncorking pressure of rifle ammo, typically 10,000 PSI or higher, produces a smooth-surfaced gas bubble. It expands too quickly to mix until it has sufficiently cooled.

An example of incandescence is your common light bulb. The electricity flows through the filament, and the filament glows due to the electrical resistance of the material involved. The filament, due to electrical resistance, is heated up until it is hot enough to be incandescent, and the glow is in the visible spectrum, which throws off … light. The filament is not consumed, it is not burning, it simply ejects photons due to the heat. Turn the light off, electrical flow stops, and the filament cools and stops emitting photons.

The muzzle flash of your rifle is the same principle. The hot gases, expanding into the cool air, emit photons from heat, not from burning powder. A flash hider hides most of this by creating turbulence. By mixing the cooler ambient air with the expanding bubble in a random pattern, there is no longer a large flat surface, or bubble, to glow.

MUZZLE DEVICES, GENERAL

There are two types of muzzle devices — flash hiders, already explained, and muzzle brakes (or compensators) that use gas differently. A third type of muzzle device is simply a place to mount a suppressor.

FLASH HIDERS

Flash hiders keep muzzle flash down in the visible spectrum. In the Infrared, they don’t do squat. In fact, a rifle may produce a visible muzzle flash only part of the time but through a thermal scope it will flash every time. Hot gas is hot gas, even if it isn’t incandescent in the visible spectrum. A thermal scope will see it every single time.

An AR barrel with no flash hider is problematic. In a rifle length 20-inch barrel it isn’t too bad, as there is enough length and time for cooling and pressure loss to keep flash manageable. Also, there are a lot of uses where the shooter doesn’t really care if there is a visible flash or not. A deer hunter, for instance, cares not one whit about muzzle flash. Target shooters are not bothered by it. Most matches are held in broad daylight, and cardboard targets aren’t going to notice muzzle flash. But the rest of us want a flash hider.

The basic A1 and A2 flash hiders do a very good job. The A2 differs only in that it has three of the slots closed, so that when you are firing prone, in a dusty environment, you will not be kicking up so much dust that everyone will be able to point and say, “Over there!” The closed bottom allows you to perform some tuning later on.

The baffles and exhaust ports are meant to change the direction of gas flow to the benefit of the shooter.

The next flash hider to consider is known as the Vortex. The real-deal, actual Vortex is made by Smith Enterprise. It's longer than the A1/A2, and has only three or four (depends on the caliber) open-ended slots. The tines of the Vortex are thicker than the slot walls of the A1/A2, and its slot is machined along a slight spiral, angled path. As a result, the Vortex does a much better job of turbulating the gas flow of the muzzle blast, thus hiding the flash. (Yes, turbulating. It's my book, I get to invent words now and then.) The one drawback is that the open ends of the tines can catch on stuff like vines, branches or gear.

Everyone from the smallest machine shop to massive offshore manufacturers have made copies of the Vortex design. I’m as much in favor as saving money as the next guy, but when it comes to intellectual property, I’m also interested in protecting it. So buy original if you can.

There are more kinds of flash hiders: ones with slots, drilled holes, ports, vanes, grooves, you name it. All of these are marketed as improvements, but between the A1/A2 and the Vortex, there isn’t a whole lot of improvement to be gained.

The Colt Competition muzzle brake has more top slots on the right than the left. That design keeps a right-handed shooter on center.

MUZZLE BRAKES

A muzzle brake is a simple thing in theory, and a difficult thing in the real world. A brake directs hot, high pressure gases, turning the gas flow into something we can use.

Newton’s Third Law tells us that for every action there is an opposite and equal reaction. When the bullet begins to move, the rifle begins to recoil. We can calculate the movement force precisely because we know the bullet’s mass and velocity, and we know the rifle’s mass and velocity. The first approximation is muzzle velocity multiplied by mass. For a .223/5.56 with a 55-grain bullet leaving at 3,000 fps, that comes to 165,000 gr. fps. The rifle weighs 7.5 pounds. There are 7,000 grains to a pound. So, our first estimate will be that the rifle will recoil at a velocity of 3.142 fps. (The actual total recoil is derived via calculus, as the bullet does not spend the entire bore time at 3,000 fps. I’ll leave that as an exercise for the really math-happy reader to solve.)

The same estimate, using a hunting rifle in .30-06, with a 180 grain bullet at 2,500 fps out of an 8-pound rifle, gives us 8.035 fps as the recoil velocity. Even if you’ve never fired an AR before, you can clearly see that the recoil it generates isn’t all that onerous.

The muzzle blast is basically a jet nozzle, and we can also calculate that. If we take a basic .223/5.56 load, with 25 grains of powder, and we burn and eject it, we have extra recoil. The hot gases jet out at over 4,000 fps, in some loads as high as 5,000 fps. We’ll use the lower figure. 25 grains (we’ll assume it all ejects at full velocity) at 4,000 fps is an additional 100,000 gr. fps in recoil. That adds 1.90 fps to the recoil velocity of the AR. (The .30-06? It adds 50 grains of powder at 4,000 fps, for an extra 3.57 fps. Ouch.)

But, what if we redirect those gases? A brake can jet them out to the sides or top, or cause them to slam into a fixed barrier, decelerating them. You can use the leverage the barrel provides, and not just negate the added gas component to recoil, but pretty much negate all the recoil. And that’s what a muzzle brake does.

You will notice that there is no mention of turbulence or of reducing flash. That’s because most muzzle brakes are actually flash enhancers. They redirect gases as smoothly and cleanly as possible. A good muzzle brake is loud, as the gases are re-directed back at you, or the guy next to you. They are dangerous, as the 4,000+ fps gases have been smoothly (smooth means efficient, and efficient means no loss of momentum) squirted up or to the sides — or both. You do not want to be standing next to someone shooting a braked rifle in any caliber.

A low profile, but effective brake, this one from PRI.

Despite the assurances of manufacturers, there is no such thing as a device that is an effective muzzle brake and flash hider. You have to pick one. The one kinda-sorta exception to this is a suppressor. It really does a good job of dampening muzzle flash, most of the time, and it does kind of reduce felt recoil. But that’s not why you buy one, is it? You buy one because it is quiet.

MUZZLE DEVICES

In the past, “muzzle devices” could mean anything from a flash hider to a blank firing adapter, screw-in chokes or a rebar cutter. Now, it means something with which to attach a suppressor.

Suppressors come in two flavors: direct-thread and QD, or quick detach. Direct thread is just that, you simply screw your suppressor onto the barrel using the same threads on which the flash hider was attached. This has the virtues of being simple, cheap and light. It also means you have to be a little more careful when using it, to make sure it stays tight. And you can’t easily go swapping it from rifle to rifle, especially when it is hot.

The Surefire suppressor mount can be a flash hider (like this) or a muzzle brake (a different part), but each has a special indexing design so your rifle has return-to-zero repeatability.

Pistol suppressors need a booster, rifles do not. On a 5.56 or 7.62, not a problem. But if you want to use a suppressor on a 9mm handgun and carbine, you’ll need two different rear caps.

That’s why suppressor manufacturers make quick detach mounting systems. The mount, or muzzle device, is screwed onto your barrel and locked in place with some sort of locking compound. The favored one currently is Rocksett. The suppressor attaches to the mount, using a fast-pitch thread and ratchet system. Once the ratchet clicks to the end, the suppressor won’t move. The advantages are, you can easily move the suppressor from rifle to rifle (each needs to have a muzzle device pre-installed) and it can also be removed and locked up, if you so desire.

The downsides are, you have to buy a muzzle device for each rifle you want to suppress. You also have the extra weight of the muzzle device. A suppressor built to use a muzzle device typically weighs more than the identical model built as a direct thread suppressor.

Muzzle devices can be flash hiders when the suppressor is off, muzzle brakes, or simply an attachment point with no extra function.

Unless you live in a state where a threaded muzzle is a no-no (and why do you live there?) then you’ll want to have something on the muzzle.

THE REACTION ROD DOES DOUBLE DUTY

In the barrel chapter, we discussed the use of the Geissele Reaction Rod for barrel installation. It turns out that the Reaction Rod is useful for more than just that. In fact, when it comes to flash hiders and suppressor muzzle devices, the Reaction Rod is a Godsend.

In the past, the work to swap a flash hider, muzzle brake or muzzle device was a pain. The easy way was to use the receiver clamshell, and clamp the upper (without bolt and carrier) in the vise, then wrench on the flash hider. While that works, if you have a particularly difficult removal (I’ve seen and worked on flash hiders that took liberal applications of heat from a propane torch as well as a big open-end wrench to remove) you are putting the torque of this work on one small, not-so-stout spot — the alignment pin and slot. The pin is the steel post in the barrel extension, the slot is just a small gap cut into the front flange of the upper receiver. The flange is not thick. The slot keeps the barrel aligned. Too much torque can enlarge the slot.

The Reaction Rod solves that problem. Simply clamp the rod into the vise, slip the barreled receiver over it, and you are putting the torque into the barrel extension, not the locator pin and slot.

Even if you never work on a suppressor, the Reaction Rod can make flash hider and muzzle brake work a lot easier.

FLASH HIDERS, ATTACHMENT

The threads on your standard .223/5.56 AR are ¹⁄₂-28. That is, the nominal thread diameter is .500 inches, and there are 28 turns to the inch of threaded section. Other calibers will have different thread pitches, in order to prevent installing the wrong (as in, undersized) flash hider onto a barrel where it can cause a problem. You can have a die of that pitch on hand, if you want to clean up the threads, but for most installations it won’t be necessary. A die is the thread-cutter that cuts the barrel threads, a tap is the tool that cuts the threads that would fit onto the barrel. I can see one instance where a ¹⁄₂-28 die would be useful, and that is if the original lathe operator cut the threads to the large side of the tolerances, and the flash hider maker cut them to the small end. You could use the tap to open up the flash hider threads, but the die is more useful, as it is somewhat adjustable for bringing down in diameter overly large threaded diameters.

Colt uses a cone washer. It is tapered on the inside and out, a section of a cone that is compressed, creating tension to hold the flash hider in place.

Two of the three washers you do not want to use on the back of your suppressor or muzzle brake. But they are just fine for use with a flash hider.

To attach a flash hider, you need a washer of some kind and a wrench. The wrench is most likely a ³⁄₄-inch open end. Flash hider washers come in three kinds — split, crush and peel. The split washer is a common industrial and hardware store type. The washer is cut into a “C” and then bent so it forms a spiral. It is heat-treated so it acts like a spring. As you tighten the flash hider down, with the washer between the flash hider and the barrel shoulder, the springiness of the washer loads the flash hider so it won’t unscrew later. This is easy, fast, simple, somewhat ugly and definitely not mil-spec.

The second washer is mil-spec, kinda. It is the crush washer. This washer is a simple circle of steel, but the flats are both angled to the bore. Think of the top of a funnel, made of steel, and the top rim cut off. As you tighten the crush washer down, the flex of the small steel cone acts to load the flash hider, keeping it from loosening.

Both of these washers have the same problem — timing. There is just none built in. If the threads of your barrel are not timed to the shoulder, then when the flash hider is tightened it may not be properly aligned. If you are using an A1, no problem, it’s all the same. But the A2 has to have the non-slot side down. The only way you can adjust the timing is to either lathe turn the barrel shoulder back, or cut the rear face of the flash hider. Luckily, the flash hider is not a hardened piece of steel and it is easy enough to do that.

Enter the peel washer. The peel washer is simply multiple layers of foil, glued together. To adjust the timing of the flash hider, use a knife to catch the edge of a layer and peel some off. The drawback of the peel washer is that it does not load the flash hider, and you have to use Loctite to secure it once you determine the proper timing.

Any flash hider installation is a “cut and try” operation. You cannot simply spin it on, torque it with a wrench, and call it done. Which brings us to the torque limits for the flash hider. The mil spec for this is spelled out in the official military torque settings section, per TM 9-1005-213-23&9. And that guide is oh so unhelpful. The recommendation is to hand tighten the flash hider and then use a wrench to turn it ¹⁄₁₄th of a turn more until it is aligned. ¹⁄₁₄th? Seriously? What that means is that almost every flash hider in existence is overtightened.

Which leads us to the High Power shooters. In Chapter 2, we discuss a very expensive barrel that is made to shoot small groups, consistently at long distances. High Power shooters aren’t required to use flash hiders on their rifles, as the rules committee allows them to shoot with bare muzzle (in case the competitor happens to reside in a State not allowing them). But those who do insist on a flash hider don’t want to be using a wrench on the muzzle, after spending a lot of money to have a primo barrel installed. These folks time a flash hider so it comes up properly aligned with hand pressure. And not much of that, either. This involves either machining the barrel shoulder or filing the rear of the flash hider, until it hand tightens to just the right spot. Then they take it off, degrease the flash hider and muzzle threads and use a liberal application of heavy-duty Loctite. That’s right, their flash hider is essentially glued in place.

Works for them.

NOVESKE PIG KX3

The Noveske is an interesting bit of gear that serves a very useful purpose. The Pig is a flash hider, but it is also a sound re-director and a gas flow adjuster all in one. It's derived from the “Krink” muzzle brake, which increased gas dwell time on an AK SBR. It also changes the nature of the muzzle blast. Namely, it directs more of the noise forward, less to the sides and back, without being a suppressor. Yes, I have determined this by carefully (oh so carefully) walking to locations that I would not advise you doing.

The secret to this working is a backwards cone inside of the larger housing. The downside is, regular disassembly and cleaning is required. I know this because a friend of mine wanted to remove his to try something else. "J," as we’ll call him, is a high-volume shooter. He has worn out barrels in practice. The Noveske would not come off. It finally took two of us, with tools, heat and a vise to wrestle it off. Strangely, it weighed a lot more than a new one we happened to have there for comparison.

It would not come apart, so Ned Christiansen took it back to his shop and split it with a wire EDM machine. Yowza! It was packed with carbon like an abused suppressor.

That’s how we know. If you have one, and you can still get it apart, take it off and clean it. If you can’t, you’ll at least know why and what the outcome will be. Kept clean, it is a great addition to your AR.

The Noveske KX3. This one left uncleaned after use and packed full of powder residue. Don’t do this, clean your pig.

The most effective muzzle brake to be had, the McArthur PRGS-1.

MUZZLE BRAKE ATTACHMENT PROCESS

The muzzle brake replaces the flash hider. Unscrew the flash hider, clean the threads and screw on the muzzle brake. Secure it by one of several methods. The first, and most elegant is, to screw the muzzle brake on until it bottoms out against the shoulder of the barrel, correctly timed for your needs. This isn’t always possible, simply because the threads of the barrel and the threads of the brake may not be in agreement. The brake/comp can bottom out upside-down for all you know.

You can use a peel washer, as with the flash hider, to adjust the timing to clock properly.

Or you can use a lock nut. This is simply a nut of the correct thread pitch, screwed on before the brake. Once the brake is on the muzzle and almost bottoms out, time it. Then unscrew the lock nut until it contacts and stops against the brake.

There is no mil-spec for this, there is no industry standard; there is only what works. The bare install — the brake on the barrel — requires a lot of work and special tools to make it fit correctly. The peel washer is easy and adjustable. The lock nut is very secure, but does take up space on the threaded portion of the muzzle meaning fewer threads by which to hold the brake.

MUZZLE BRAKE ATTACHMENT DYNAMICS

Any muzzle brake has two components to its action: forward and up. The upward force dampens the muzzle rise, which is created by the offset lever of stock and body. Even the in-line stock of the AR-15 can create upwards movement. You see, the typical military stance, and one adopted by a lot of shooters, in effect negates the in-line design.

The military stance uses what I call the “bazooka hold.” The rifle is mounted as high as possible, with the toe of the stock touching, and the head upright. This means that the contact point of the stock, on your body, is off-line of the thrust of recoil, which is directly back through the buffer tube. The rifle pivots up, since the contact point is below the centerline.

How much it pivots depends on how tightly you hold it, how much of the stock toe is in contact, and the power of the load you are firing. There is also a slight lateral movement, outwards (to the right for a right-handed shooter, left for a southpaw) due to the contact point being off your own centerline. The rifle recoils, pushing on your right side, your body twists slightly in response and the muzzle wavers outboard.

The muzzle brake has to be timed at a slight angle, with the ports relieved similarly, so as to counteract the movement. Since this movement is different for every person, it becomes a personal detail. Also, if your shooting style changes, or you change the load — powder, weight, bullet — the gas flow of the muzzle and the brake changes and must be re-tuned.

The other component is forward force. As the gas exits the bore and enters the brake, it crashes into the baffles, the faces of the slots or ports cut into the brake. The impact of the gas jolts the rifle forward, counteracting the rearward recoil. The amount of forward jolt depends on the barrel length (shorter means higher pressures at uncorking) powder charge (more powder means more gas mass) and the size of the clearance holes in the face plates (larger holes mean less face plate surface area, thus less jolt).

The simplest method to lessen the forward force is to bore out the clearance holes. Alas, this requires a lathe. Sure, you could just reach in with a hand reamer in a T-handle, or a dremel tool, but if you open the holes off-center, you will change the characteristics of the comp, and probably not for the better.

The easiest way, if you don’t own a lathe, is to change the powder you use, and/or the powder charge. This becomes an interesting dance, as you have to meet a power requirement in 3-Gun or multi-gun competition. You need a reliable and accurate load. And you want a balanced recoil-dampening comp.

Frankly, for most people, tuning a comp is a waste of time. Until you’ve shot enough to have worn out your first barrel, all comps are the same. They will all dampen recoil. They will all not quite match your shooting form and style. And your shooting form and style, until you have had enough experience, will change on its own more than the differences between the comps.

Once you have settled on a particular style, and use it consistently, then you can get fussy about tuning comps. Here’s how to do that.

The JP Enterprise “Tank” brake. For when you absolutely, positively, have to clear off the benches on either side of you.

TUNING UP AND OUTBOARD

Determine your stance and form. Set up a shooting box — a defined area marked out on the ground — with a target 10 yards away from this spot. Take your time to get comfortable. Practice running up to and into the box, stop suddenly while bringing the rifle onto the target. If your gun club won’t allow this, find one that does, because this is a lot of what you’ll be doing in competition.

Once you have found a consistent position, run up to and into the box again, plant and aim. And stop. Load the rifle, without moving your feet. Lift the rifle and fire five rounds into the center of the target as quickly as you can.

Unload and analyze. Look at the group. Is it centered? Is it even? Or did the rounds track up and to the right? Recall what the dot or sights did during the five shots. Did the rifle recoil straight up? Angled to the side? Stay put? You are doing this not to improve your speed, but analyze the recoil track. If the rifle went straight up and down, cool. Your work is mostly done. If it just hung on the target with no upwards or lateral movement, you’re done here. Your comp is as correctly tuned as it can be to your current stance and skill level. Get to practicing for the next match. If not, you have some adjustments to make.

If the rifle tracked up and to the right (right-handed shooters) then you have to tilt the comp to the right. Not much, just a bit. Recall how the dot or sights tracked. The high-right group happened at a particular angle. Select a tilt on the brake that is half the angle the sights moved.

This is where muzzle brake installation method can make a difference. Make changes with the rifle unloaded, ideally held in a vise to hold the Reaction Rod (see sidebar earlier in this chapter). Eyeball the angle — use a pencil, held in one of the baffle slots, to indicate the attitude — and unscrew the brake. If you torqued the brake down bare, you’ll need a peel washer. Remove the brake, install the peel washer and hand tighten. Note the angle and start peeling off layers of the washer until the brake is no longer tilted to the outboard side. You will have to unscrew the brake to its new position by the smallest amount, which means probably just a few layers of the peel washer.

If the brake was originally installed with a peel washer, add just a few layers to tilt it to the right, or remove most of the washer, turning it nearly a full rotation.

If you used a lock nut, life is easier. Loosen the lock nut, tilt the bake, retighten the lock nut.

Get back down to the range and repeat the drill. Keep adjusting it until you have the angle right for you.

There is a drawback as related to competition. Clever stage designers will lay out the targets and obstacles so you can’t always get into a comfortable, identical, firing stance. They will make you shoot from awkward positions. If your stance changes, the brake angle you need changes. So, in some situations, you may find that not only is the brake not helping you, it may actually be a hindrance.

That’s the main reason I worked myself into a more-or-less neutral firing stance and don’t use the “bazooka hold.” With the brake vertical, I can count on it being less of a problem in those awkward stage locations.

TUNING FORWARD

The most effective way to tune a brake for decreasing forward thrust is to bore out the clearance holes in a lathe. Lacking such a machine tool, your option is to change powder charge, bullet weight, or both. The two variables you can control are the amount of powder you use, and the amount of gas mass produced at the muzzle. The caveat here is that unless you also adjust burn rate (more powder, slower rate) you will simply be increasing recoil and velocity.

The second option is to change bullet weight. Here you want a heavier bullet to reduce gas mass, since you won’t need as much powder to boot a hefty projectile up to the threshold velocity for the power you need.

This is what Production Division handgun competition shooters do. Instead of loading a 115- or 124-grain bullet to the threshold velocity, they load a 147- or 150-grain to threshold. At the threshold, they get the same power factor, which is weight times speed. But the heavier bullet uses less powder, and as a result there is less of a jet-nozzle effect from the gases. You aren’t scored on the gas component of recoil, but your hands feel the difference.

With the threshold power factor at 125, a 124-grain bullet needs to go no less than 1,008 fps. A 147-grainer needs to speed along at less than 850 fps. A typical powder charge for the 124-grain bullet is 5 grains of powder. For the 147 to make 850 fps, the charge is more like 3.4 grains. The one-third less powder weight alone will make the jet-nozzle effect much less.

Similarly with the .223/5.56. A 55-grain bullet needs to be going no less than 3,000 fps. That can be done with as little as 23 grains of powder. However, a 77-grain bullet needs to only make 1950 fps. That is absurdly slow, but demonstrates the difference since you can get a 77-grain bullet out the muzzle with as little as 18 grains of powder. (Of course, in this example, you risk producing so little gas pressure that you don’t cycle the rifle, but that’s not the problem right now.)

Another alternative is to try different brakes on other shooters’ rifles. If you find an off-the-shelf brake that produces just the right amount of forward thrust, buy it.

SUPPRESSOR MOUNTS

Suppressor mounts come in three types: flash hiders, muzzle brakes, and suppressor-specific. Of the three, the latter is actually the one not requiring timing. All brakes need timing, and some flash hider mounts do too, but not because of hiding flash. It’s because they must control vibrational dynamics and ensure return-to-zero mount and dismount.

Suppressor-specific mounts have a much harder life than flash hiders and muzzle brakes. Suppressors work, in part, by turning noise into heat. A suppressor gets hot, very hot, and the mount simply bakes in the heat. As a result, you cannot depend simply on torque to keep the mount tight. Threaded fasteners work by using the threads as tiny springs. The threads flex as you torque up a part. One of the attributes of steel is that when it gets hot enough the spring tension of a part can change. So if you simply wring it on “farmer tight” and blast away, it may come loose.

Top, the AAC, bottom the YHM muzzle device for mounting suppressors. Each manufacturer has a proprietary design and there is no “one size fits all” mount.

You need a thread-locking compound of some kind. The first thought is Loctite. However, when Loctite gets too hot, the compound breaks down, the sheet becomes a granular layer and it loses its locking ability. That’s actually how you remove something held in place with Loctite — you heat it up. Now, the decrease isn’t a complete loss of strength. If you have used a propane torch to burn out Loctite, the granular layer that remains will still interfere with self-loosening. You’ll have to work to remove the part. But it isn’t as tight as it was.

Rocksett reacts differently. While the sheet will heat up, it retains strength and, when it cools, reforms a sheet holding the threads tight. To remove Rocksett, soak the joint in water at least overnight, a full day is better.

The process is similar to a muzzle brake, with one exception — flat shims. Many of the makers offer shim washers that are flat. If you use non-flat shims (and a peel washer is the very definition of non-flat) you may tip the mount when you tighten it in place. That can be very bad. A tipped mount means a tipped suppressor and that risks a baffle strike, which can be annoying or scrap a suppressor — costing you a grand and six month’s waiting.

Surefire uses stackable, color-coded washers to let you properly time your suppressor.

Clean the thread, barrel and mount. Hand install the mount. Check clocking, as with the muzzle brake above. Use the flat washers to adjust timing until it aligns properly when torqued. Consult the instructions that came with the suppressor for the correct torque value. If none is listed, you can go with ¹⁄₈th more of a turn with the open-end wrench, once it is hand tight. Then, there’s one more step before you can lock things down.

Get out the suppressor that will be mounted on that device, and your Geissele alignment rod. What, you don’t have a Geissele alignment rod? Then set everything aside until you do. Yes, you’ll have to wait for a week or so for it to be delivered, but in the event you discover that your suppressor was seriously misaligned, it will be the best week you ever waited.

Make sure the rifle is unloaded. Mount the suppressor. Slide the rod in and check alignment. If it passes muster, then you can proceed. If it doesn’t, make it straight.

Remove the suppressor, mount and shims, if any. Keep the shims together in order. Use an aerosol degreaser, making everything squeaky-clean dry. Apply Rocksett to the barrel threads and let the goo ooze down around the threads. Cover them from front to back. Slide the shims on, then hand screw the mount into place. Next, use your wrench to torque it down. Each manufacturer has their own idea of suitable torque limits for the mount. If they don’t list a specific value, assume that 1/8th of a turn will be the correct amount.

Once done, leave it alone. Unlike some types of Loctite, which can set in seconds, Rocksett needs 24 hours to properly cure. Shooting too soon can weaken the bond. If it won’t align, either the threads are not cut axial and straight or there is a mismatch in the shoulders of the barrel and the mount. Specifically, in the latter, the thread ending portion.

Threads must be cut on a lathe, so the center of the threaded surface is in the same place as the center of the bore, not the exterior of the barrel. A good lathe operator can use a plug in the bore, and an index gage, to adjust the lathe so the barrel is spinning around the center of the bore. That allows them to cut the threads on-center to the bore. Threads cut while using the barrel exterior as the index may result in the center of the threads (and thus the mount, and suppressor) off-center from the bore by a few thousandths of an inch. This may not be a problem if the clearance holes in the baffles are larger than the error in machining.

However, the thread surface also has to be straight. That is, the threads cannot be tipped in relation to the axis of the bore. That is a big no-no. A very small angle adds up to a big misalignment 7 inches later when the bullet arrives at the front plate of the suppressor.

A mis-machined thread is not something you can correct with hand tools. In fact, you can’t do anything but find a good machinist to shorten the barrel by the threaded amount, and then do a proper threading job. If the threaded portion of the existing barrel goes back further than the shortest barrel length allowed by law (as 16-inch carbine barrels do) then you are out of luck.

However, if the barrel thread shoulder and the mount shoulder are in disagreement, you can work with that.

THREAD TALK

When a round object such as a barrel is threaded, the surface is turned down to the major diameter of the threads. That is, the size of the thread tops. For an AR-15 barrel, that dimension is .500 inches. The threading tool is applied and the threads are cut. However, the job is not all done. You see, the threading tool can’t cut the threads right up to the shoulder created by the first cut. There’s a short section that is still 0.500" in diameter that lacks a thread.

A good machinist uses a parting tool to make a relief cut at the back of the threads. That takes the 0.500 inch section down to the depth of the thread bottom, below the minor diameter of the threads.

On the mount, the threads are cut the same way, but on the inside. The bore is threaded all the way to the rear face of the mount. Without a relief cut behind the threads, the mount can stop before contacting the barrel shoulder. That tips the mount, and is a very insecure torquing point.

If that is the situation for your rifle mount setup, you need a lathe to correct the barrel. And you have to remove the barrel to do that. Or, you can simply take the mount to your local machinist, discuss the problem, and have him relieve the rear of the mount, clearing the offending section of barrel thread.

If after all that your mount still doesn’t tighten straight, the threads are misaligned and you need a new barrel.

Mount makers realize that a lot of barrels aren’t cut properly, so they tend to put extra effort in to make sure theirs is right.

PINNED AND WELDED

The term “pinned and welded” comes to us courtesy the moronic NFA, or National Firearms Act of 1934. Barrels on rifles and shotguns that are short are referred to as “short barreled rifles” (SBR) or “short barreled shotguns” (SBS). These are controlled as if they were machine guns and require a transfer approval from the Feds, and a one-time payment of $200 tax to the same.

A rifle may not have a barrel shorter than 16 inches, without transfer approval and taxation. Anything over 16 inches is fine, and anything under is not. Colt ships rifles with 16.1" barrels. Other makers ship 16.25" barrels. As long as it is over, it is kosher. Under, and it is taxable, and must be approved.

But the barrel makers are set up to make scads of barrels that are 14.5" long, because that is the military spec. And we discussed why in the barrel chapter. So, there you are, looking at a dirt-cheap 14.5-inch barrel at a gun show, but can’t buy it because it is too short. What to do?

A quirk in the barrel length interpretation is that if a part is permanently attached to the barrel making it effectively longer than 16 inches, the barrel is considered longer than 16 inches. So, if you permanently attach a flash hider to your 14.5-inch barrel, giving it a net length of 16+ inches, you’ve done it. I have to emphasis “net length” because the threaded portions of both the barrel and flash hider will overlap, and you’ll lose those. So, a 14.5-inch barrel needs a flash hider that has an overall length of something like 2.5 inches, so you end up with a 16-inch barrel or longer.

Another concern is what is considered “permanently” attached. The ATF regulations that cover this are both specific and general. They are specific in that there are no chemical fasteners or bonding agents that meet their standards. No epoxy, Loctite, JB Weld, none of that will do for them. They want a high-temperature solder, with a melting point of 1125 degrees Fahrenheit or more, or a welded bond. Heating a barrel muzzle and device to 1125 degrees-plus is not good for the barrel. Welding is the answer.

One way is to tack-weld it at three or four points equidistant around the barrel. A continuous weld would be better, but they don’t require it. Another way is the “pin and weld” method. Here, you fit the flash hider, muzzle device, muzzle brake or simple extension to the barrel. Drill a hole through the flash hider, but not through the barrel. The idea is to drill deep enough to “dimple” the barrel at the threads or the shank behind the threads. Press a short section of rod into the hole, so it rests in the dimple, and would prevent the flash hider being unscrewed. Then, the last step is to weld a bead of steel over the end of the section of rod, trapping it in place, thus preventing the flash hider from coming unscrewed.

This locks the flash hider in place and extends the barrel without pumping any more heat into it than absolutely necessary.

There are drawbacks, however. Once the flash hider (or whatever) is permanently attached, you cannot remove anything attached to the barrel that is smaller than the flash hider. Your gas block or front sight is trapped in place, as is the barrel nut assembly. Once the device is pinned and welded, the barrel is permanently trapped the way it is.

As a result, you have to build it, and then see if it works. If it doesn’t, you must undo the weld to make any changes. And when you do so, you have technically created an SBR.

You can’t legally build an SBR “temporarily” and then once it works properly, pin and weld it. But if you own an SBR you can build an upper for it, test it, debug it and then pin-and-weld the barrel, putting the resultant upper on a non-SBR.

As a result, there is a good case to be made for the non-pinned design of gas block and front sight assembly, as you can change those even with a pinned-and-welded barrel.

CHAPTER 11
SUPPRESSORS

You’ve made the choice, taken the plunge and waited patiently. Your new suppressor is here, and you are eager to mount it on your AR and get to work. Hold on, you still have a bit of work to do.

If you are going to spend any time at all with suppressors, invest in two tools from Geissele — the Reaction Rod and the alignment gauge.

As discussed in earlier chapters, the Reaction Rod will allow you to change muzzle devices without having to strip the upper, hold it in a clamshell or clamp the barrel. The alignment gauge will tell you if the muzzle device is on straight.

You do not want to be putting frangible ammo through your suppressor. This is not to blame Federal, they make good stuff, but frangibles and suppressors are trouble.

When mounting flash hiders, thread straightness isn’t an issue. No flash hider ever made will be so out of alignment that it will cause a problem. Muzzle brakes are made with sufficient tolerance to avoid problems. (In fact, they are de-tuned because there’s so much gas you don’t need to be super-efficient.)

But suppressors? You can bust one on your first range trip if it is out of alignment.

To swap a flash hider out to uncover threads, or replace it with a suppressor-specific muzzle device, use the Reaction Rod. Especially if you have a free-float aluminum handguard and don’t want to be taking it off just to swap out the gizmo on the end of your muzzle.

Alignment gauges are a different subject.

The gauge is a straight, centerless ground, hardened steel rod used to make sure your suppressor is on straight. The process goes like this. Unload the rifle and hold the upper in a vise, fixture or cradle. If you have a direct thread suppressor, screw it on. If you have one that requires a specific mount, install it hand tight and mount the suppressor on it.

This is what frangible looks like. Only use it when your suppressor is off.

Slide the Geissele gauge down the bore, leaving the end of the rod poke out through the hole in the front cap of the suppressor. Geissele rates gauge indication by three classes: Complete Pass, Partial Fail, and Complete Fail.

Ideally, the rod will ride dead-center through the hole in the suppressor cap. This means the suppressor is straight and centered, or a Complete Pass.

The more off-center the rod is, the worse it may be for you. An off-center rod is a Partial Fail, but not all Partial Fails mean you can’t use it. It just means the suppressor isn’t dead center. Slight off center but not anywhere close to touching is probably OK, but when it comes to judging this you’re on your own. Me, I want a Complete Pass.

The NT on the headstamp means it is a lead-free load, including the primer. Some ranges require it.

If the rod touches the edge of the front cap hole, this is a Complete Fail. Don’t shoot it, you’ll have bullets brushing baffles, or worse. I’ve seen muzzle threads cut so badly that the Geissele gauge would not pass through the suppressor. It touched one or more baffles so hard that it bound in place.

FIXING THREADS

As covered in the previous chapter, threads are cut by lathe-turning the external diameter of the threads in the barrel, then applying a thread-cutting tool.

If you have a suppressed barrel with a twist other than ¹⁄₇-inches, you must pay attention to what bullets your ammo holds. The span from 55 to 90 grains matters.

The normal thread pitch for an AR is 1/2x28. That is, a .500-inch thread with 28 turns to the inch. The barrel muzzle is turned down to 0.500 inches and the threads are cut. But the thread-cutting tool can’t cut right up to the shoulder. Just like mowing your lawn, you can’t cut that last inch or so, requiring you to go back with an edger.

The threaded muzzle ends up with a partial shaft of half-a-thread, with the rest 0.500 inches in diameter. This matters because the muzzle device may also be threaded all the way out. Unlike the barrel, the muzzle device threads go all the way out the back. When you screw the muzzle device on, the last bit of thread on the device hits the stop point of the thread groove on the barrel and the shoulders don’t make contact. Applying torque only tips the device as it stops at the thread groove end.

It deserves mentioning again that good barrel makers use a parting tool to make a relief cut against the shoulder, down to the base diameter of the threads.

This doesn’t matter with flash hiders and brakes because these use a washer to help lock the gizmo in place. The washer stops the device before it hits thread bottom. Too, a very slightly tipped flash hider means nothing.

The increased dwell time the suppressor creates causes extra stress on the rifle and can blow gas in your face.

But a 7-inch long suppressor, designed as a close fit to scavenge gases, can be big trouble if tilted.

To solve this, a machinist indexes and centers the barrel in a lathe, then cleans up the ugly threading job, making sure there is a sufficient relief cut on the backside of the threads. If you don’t have a lathe or access to one, use flat washers to create an artificial shoulder that is further forward, preventing the muzzle device threads from hitting the end of the thread groove.

BIGGER IS GOOD, SMALLER IS BAD

You can use a thread adapter to mount a suppressor meant for a larger caliber onto a smaller caliber rifle. That is, if you have a suppressor for 7.62x51, you can use a thread adapter to mount it on a rifle in .300 Blackout, 5.56, 6.5, 6.8, etc. What you cannot do (and no one makes such a beast, for understandable reasons) is use an adapter to mount a suppressor meant for a 5.56, on a rifle chambered in something .30 caliber.

Suppressor covers keep heat off of you, out of sight and contained in the can.

That would be stupid.

Now, there are mismatches that are not so apparent. The common 1/2x28 thread pitch of the .223/5.56 is the same pitch used in the .22LR. If you were to use a rimfire suppressor on your AR in .223/5.56, you would quickly be sorry. The rimfire suppressor is meant to handle the muzzle pressure of a .22LR, which would be a few thousand PSI. The uncorking pressure of an AR can be as high as 17,000 PSI. You’d bulge your little silencer like a can of beans that had been on the shelf too long.

Conversely, using a sealed .223/5.56 suppressor — often called “cans” by shooters — on a rimfire is not smart. The rimfire can comes apart because the ammo is incredibly grubby and you need to clean it on a regular basis. Centerfire suppressors run so hot (and the cartridge so clean, by comparison) that you do not need to clean them.

The last problem to watch out for is 9mm. The standard 9mm thread pitch is also 1/2x28. If you were to screw a rimfire or .223/5.56 suppressor on your 9mm, you would be sorry almost immediately. The baffles simply wouldn’t have enough clearance, and the first bullet would crash into the first baffle. From there it would get worse.

SUPPRESSOR COVERS

The fashionable thing to use with a suppressor is a cover. It keeps you from inadvertently burning yourself and others, and keeps the heat mirage under control, out of your line of sight.

This it accomplishes by trapping the heat in the suppressor, allowing it to escape only through the front cap, and by heat transfer back into the barrel. High fashion and operational advantages cost money. Covers are useful, but keep the heat in mind.

AMMO TO USE

Generally speaking, if it is OK to use ammunition with the suppressor off, it is OK to use it with the suppressor on. But there are exceptions. One is twist and bullet length. The classic example is the M855 in a rifle with a ¹⁄₁₂ twist. That bullet is too long to be properly stabilized and will end up going through a 25-yard target sideways.

Coming out of a rifle with just a flash hider, it’s no problem. But with a muzzle brake or a suppressor, the bullet can be wobbling (the technical term is yaw) such that it hits a baffle. Once it does that, there’s no guarantee it will keep going straight out the end.

The other ammo type is known as frangible. These are bullets made of powdered copper, compressed into a bullet shape, and meant to break apart into dust on steel targets and backstops. The strength of frangible is that it is markedly safer to use on steel targets, in indoor ranges and in shoothouses. Their weakness is, they are frangible. They can break during feeding and while firing, and have left some barrels in pieces (the bullet, not the barrel). In a training situation, with a non-suppressed firearm, it is no big deal. In a suppressor, you’re just asking for a baffle strike.

There is one load that features a powdered core and a jacket made by Federal for use by the Navy called the MK311. It is rare, expensive and probably something you won’t need.

Do not confuse sintered/powdered frangible ammunition with all-copper ammo. Bullets made of solid rods of copper are not frangible, and will penetrate like ball ammo.

GAS FLOW

As mentioned in the bolt and carrier chapter, the use of a suppressor increases the dwell time of gas in the system. To deal with this, you have to dial back the gas flow. This can be troublesome if you want to swap back and forth between suppressed and unsuppressed.

ADJUSTABLE GAS BLOCK

One way to deal with it is to install a piston system with an adjustable gas flow. Another is to install the POF adjustable gas block. It comes with a wrench that fits the adjustment nut, and you simply adjust and experiment at the range until you find the settings that your rifle needs, with or without your suppressor.

To install, the POF is just like any other gas block, except it comes complete with a gas tube and instructions. Once on, it would be prudent to experiment and keep notes on what settings you need with various loads and suppressors.

GEMTECH CARRIER

The Gemtech carrier has a suppressed/unsuppressed setting on its side. You simply assemble your bolt into the Gemtech carrier, set the port to one or the other, place the bolt/carrier into your rifle and get shooting. If switching to the other setting, unload, open the rifle, pull the carrier out, use a screwdriver to switch to the other, reinstall and get back to it.

The Gemtech carrier offers a two-position switch, suppressed and unsuppressed.

The Gemtech carrier vents more gas in the suppressed setting, which offsets the dwell time, keeping carrier velocity down to normal rates. Yes, the venting gas does add to the noise, but it is all of one decibel, so I think you can live with that.

Anytime you want to swap, you simply assemble the Gemtech carrier into the other rifle, using that rifle’s bolt, and you’re back in business.

SUN DEVIL ADIGS

Sun Devil takes a different approach. The ADIGS is a replacement carrier key that doesn’t vent excess gas, but rather reduces gas flow into the carrier. Unlike the Gemtech carrier, the ADIGS is a one-setting part. You can swap back and forth, but it isn’t as repeatable a system. Install the ADIGS on a carrier. Tune the carrier and the rifle’s bolt to suppressed use. If you want to go back to unsuppressed mode, swap the ADIGS-equipped carrier for the one that was in the rifle to start with.

The ADIGS gas flow may not be exactly correct for the next rifle you put it in, so I can see this being more of a dedicated part for one rifle. To that end, it is less costly than the Gemtech carrier.

The Sun Devil ADIGS (in cutaway view, the actual one is whole) throttles the gas flow into the carrier. That small setscrew is the adjustment, so it isn’t easily switched from one setting to another.

By keeping gas from entering the carrier, the ADIGS decreases the effect of increased gas dwell time. Note that the pressure inside the key itself is not reduced, but the produced thrust is minimal compared to the expansion chamber thrust in the center of the carrier.

INNOVATIVE ARMS W.A.R.

Innovative Arms makes an upper that has a user-switchable gas flow setting. The lever, on the upper left side of the receiver, has three settings — normal, reduced and no gas flow. It uses a proprietary gas tube requiring your rifle be built on it. But since it is otherwise a normal M4 flat-top upper receiver, that is not a problem.

The Innovative Arms WAR upper has a suppressor switch built into the receiver.

This is what a suppressor looks like when you abuse it until it breaks.

SUMMARY

This is not an exhaustive list of products, just the ones I have had a chance to try out. One thing you have to keep in mind when you adjust gas flow, there is no “one size fits all” setting. Even with piston-driven rifles, there are regular and suppressed settings. And any adjustable system you incorporate into your build is a proprietary design. There is no universal or mil-spec adjustment, and the services do not make adjustments. The Mk18, for example, a select-fire build based on the M16/M4, is an SBR that is used most of the time with a suppressor. But it does not have any gas adjustment parts on it and the military is willing to accept a shorter (potentially) service life as a result. They expect end-users to simply adjust to the differences.

CHAPTER 12
LOWER INTERNALS

You can invest in a standard lower parts kit (also known as the LPK) or a premium trigger set. The safety comes in your choice of regular or ambidextrous. I’m not a big fan of ambidextrous triggers, simply because my trigger finger tends to rest in the space occupied by the offside lever on such a design.

The rear takedown pin (covered in Chapter 4) must be in place as you install the stock, there’s no way to go back and do it after the stock is on. The front is different.

FRONT TAKEDOWN PIN INSTALLATION

The dual push pin system of the M16, including the AR-15s that fit them, use nominal 0.250 inch diameter pins with machined heads. The thick head pin is the front, flat head the rear. These have grooves machined into the side where the detent pin rides. The groove has two small depressions at each end. The depressions keep the pin in place when fully opened or closed. To allow the upper to be removed, the groove is closed on each end so the pins do not leave the lower when they are pressed out.

CMMG packs their lower parts kits in color-coded plastic bags. That way you can have just the parts you need, for the task at hand.

A long time ago, in a galaxy far, far away, Colt manufactured AR-15 rifles for the non-military market with the infamous “large pin” in the front position. (These were made from the early 1970’s to the early 2000’s.) This pin is ⁵⁄₁₆ inches in diameter, or nominal .312 inches. The center of its pin hole is offset from that of a regular small pin. The large pin does not use a spring and plunger, but instead is drilled and tapped on the end to the left side of the receiver. Colt fitted a screw threaded bolt there. The head of the large pin and the screw-thread bolt are slotted for screwdrivers. To disassemble the Colt large pin upper, you need a pair of large blade screwdrivers. It is possible to use adapter pins to fit the mismatch together. That is, a large pin and the other a small pin. But it is really not worth it unless you are really stuck with one due to local laws. It's usually best to leave a large head upper and lower assembled as a set.

Installing or removing the front takedown pin takes a bit of fussing. Starting from a bare receiver, you’ll need the spring and detent, front takedown pin (the front has a flat on the side of the pin head) a ¹⁄₈- or ³⁄₃₂-inch drift punch and the assembly tool.

ASSEMBLING THE LOWER, FRONT TAKEDOWN PIN

Insert the assembly tool into the receiver takedown holes from the left side. Use the tool with the bored hole in the lower receiver pin holes. Push the spring through the hole, into the receiver. Depress the detent. Use the punch to compress the detent and spring. When these have been compressed far enough for the installation tool to turn, rotate it a quarter-turn. The detent and spring are now trapped in the receiver. Remove the punch.

Some parts are, shall we say, marginal. The mag catch on the right kept dropping magazines, and it’s no wonder why. The locking edge is so rounded it’s a miracle it worked at all.

If the receiver lacks a buttstock, stand it on the rear flat. However, one with a buttstock may have to be stood or placed on the seat of your chair, between your legs. Make an inverted “V” with your left hand thumb and forefinger. Place your fingers over the tool at the location of the detent. With your right hand holding the front takedown pin, use the pin to press the assembly tool out of the receiver, while using that V shape of your fingers to keep everything compressed.

You want to prevent the detent and spring from launching themselves. Once down, the detent will snap into the groove (unless you pressed the takedown pin in groove-side toward the detent, in which case it is already captured) and the assembly is done.

Spare parts are good to have. This broken hammer pin brought this rifle to a complete stop.

To remove the pin, get an angled edge inside the groove to lever the detent back. A ¹⁄₈-inch Allen wrench, with the inside edge of the short leg filed on an angle, is the preferred tool. A small screwdriver like those used on eyeglasses will also serve the purpose. The trick is to lever the detent back so it no longer captures the front takedown pin. Once the detent is compressed, rotate the takedown pin. Cover the area with your free hand when you pull the detent out of the lower. Failing to cover this spot almost assuredly results in the detent and spring launching across the room, lost forever to the search party you’ve assembled to find it.

PISTOL GRIP INSTALLATION

The pistol grip captures the safety/selector spring. Take that spring and wrap a tiny little triangle of masking tape around the end. This will let you stuff it into the pistol grip, keeping it from falling out.

Next, slide the screw and washer into the pistol grip, holding in place with a screwdriver.

The trick here is to not push the pistol grip all the way down onto the receiver flange. Doing so leaves the screw without guidance, causing it to wobble back and forth. Press the pistol grip on only far enough that it won’t fall off, lining it up by eye. The gap between the inside of the pistol grip and the receiver creates an alignment for the screw. Gently rotate the screw until you feel the threads catch. If you are too heavy handed, you can cross-thread it, and make a mess of your lower receiver.

This is one of the Colt rifles with the two-headed hydra takedown pin. Leave it alone and build on something else.

Once the threads catch, and you have the screw turned in a few turns, push the pistol grip all the way down, making sure you don’t pinch the spring and that the selector plunger is still in its seat. Tighten, and you’re done.

MAG CATCH TRICK

The easiest way to install the mag catch is to use two buttons for the job. Drop the spring into the hole. Press one button in. Then push the second button down on top of the first one, depressing it deeper into the hole. Screw the L-shaped catch and shaft in from the other side. You want the tip of the threaded shaft to be flush with the first button, and no more.

Check that the edges of the catch aren’t rounded, a condition which can cause magazines to fall out.

UPPER TO LOWER FIT

There is no reason on this green earth to screw around with fitting uppers to lowers. Yes, the military does it, but that doesn’t mean it’s necessary.

Uppers and lowers fit together, more or less. You see, the dimensions are available, but the exact specs aren’t, unless you are an honest-to-goodness military supplier. So just check fit. You don’t even have to install takedown pins in the lower to check the fit. Slip the upper onto the lower. Line up the holes and slide the front takedown pin through. Note the fit of the rear pin. Is it too tight for the pin to pass through? Try a different set. Do the upper and lower have excessive wobble? Same thing.

This is easy enough to do, and can be done in a gun shop. Bring your lower (just the lower) in to check the fit when buying a new upper. Then again, the current state of manufacturing, with everyone using CNC machining centers, means that mismatches are far less common. Most everything fits snug. You can also buy an upper with your lower, and have the retailer or supply house fit the pair before shipping.

Take five minutes to check the fit. Life is too short to have a wobbly AR.

Standard LPKs deliver a mil-spec trigger pull and look. If you want something else, you’ll have to hunt down the parts that give you the look or performance you desire.

If you need a hammer to get the rear takedown pin in or out, the fit is too tight. Uppers and lowers are common and cheap now, make sure yours fit before you leave the store.

CHAPTER 13
PISTON CONVERSIONS

While the first wave of controversy and angst have faded, there is still steady interest in piston-driven ARs. For the longest time, ARs were direct impingement, or DI, meaning gases are channeled all the way back to the receiver where the carrier is blown back. In a piston system, the gases are diverted only as far as it takes to push on a rod. That rod then pushes on the carrier, driving the system.

The rod can be segmented, with the short section pushing the longer. Or it can be full-length, with gas pushing at one end, the other end moving the carrier. It can even be attached to the carrier, as PWS does.

The idea is the same: to keep hot, powder residue-laden gases out of the receiver.

Before we go any further, let’s make a few things clear. Piston systems do not run cooler. Heat is heat. The heat you transfer back to the receiver via gas is simply transferred to the gas block in the piston system, where it pushes on a piston. Yes, the receiver will be marginally cooler, but it is cooler because the gas block and piston rod are heated instead. This can be significant, causing the gas block to become so hot as to raise a blister.

Piston systems add weight. Some more than others, but they all add some. It can’t be avoided because the gas tube on the DI system is so light that nothing mechanical could be lighter and still function. Some piston designs don’t add much weight, but they do add some.

Piston systems can affect accuracy. Again, some not much, and even those that do, the change is probably not as significant as shooter error. Let’s take a theoretical example, a rifle that is a good, solid 1 MOA performer. Put it in the hands of someone who is an average shooter, who can deliver 3 MOA. If we install a piston system/conversion that adds 0.5 MOA to the group size just from the vibrations of the extra parts, is the shooter going to notice? Probably not. After all, the rifle just went from 1.0 to 1.5 MOA in its potential, in the hands of someone who can only shoot 3 MOA. If the shooter starts shooting 3.5 MOA groups, will they even be able to tell?

The CMMG piston conversion gas block in position on the barrel with the handguard cup in place. If you are building a rifle with a free-float barrel, you won’t need the handguard cup.

Don’t worry about the theoretical changes in accuracy a piston conversion may or may not bring with it.

There is one big advantage that piston systems offer and that is adjustability. When you start using suppressors, adjustability matters. The increased dwell time created by suppressors can be offset by throttling back gas flow from the gas block to the piston itself.

The AR can be converted to a piston system in part because of design, but also the desire on the part of experimenters to make a conversion as easy as possible. A modification to an AR which involves a machine shop, welding, re-anodizing or other expensive and non-reversible changes would not have much appeal. At least not unless the advantages gained are huge. As a result, piston designers were careful to make the conversion as easy as possible, installable without modifications to the rifle — and reversible. Should you install a piston system and find you don’t like it, you can always remove it, put the old parts back, and no one will be the wiser.

The Adams Arms (old style) piston conversion in place.

The Ares, a very low-profile piston conversion that does not need or use a replacement gas block.

One aspect of the piston conversion that you cannot avoid is a new carrier. The piston system does not need a gas key. But it does need a place for the piston to push against. One of the first conversions by Adams Arms used a replacement key on which the piston could push. You removed the old key, and installed the new one on your existing carrier.

It worked, but it was not optimal, and it was viewed with some suspicion by shooters. Adams changed to a new carrier with an integral thrust shoulder, and all other piston conversion designs and kits have done the same since.

PISTON CONVERSION BASICS

Regardless of which conversion system you use, there is some preliminary work. Strip the rifle upper receiver bare, forward of the upper receiver. That is, remove the flash hider/muzzle device, front sight assembly or gas block, gas tube and handguards.

Only remove the delta ring assembly and barrel nut if you are changing to new handguards. The gas block or front sight assembly has to come off as the piston system replaces it. The flash hider has to come off because that’s the only way you can get the gas block or sight off. The handguards have to come off because you need the elbow room to position and fit the piston system. Often, when changing to a piston system, shooters also change to a new, free-float handguard, requiring removal of the delta ring assembly.

Here’s a pro tip. Given the amount of work involved, consider building a new, replacement upper receiver from parts. That way, you’d have two uppers, one DI, and one piston, and you could compare the two at the range. And since you have to strip the old receiver down, we will be looking at the installation of a piston conversion from the stripped-down point, as if you were building it up new anyway, because that gives us a common starting point.

If you are going to change to a free-float handguard, and that handguard uses a barrel nut that isn’t the standard one, you’ll have to remove the old and replace it with the new. At that point, you truly are building up the receiver from scratch. Not all free-float handguards will clear the hardware for all piston systems. It may take some research and testing on your part to find a combination that agree. I’d offer a chart, but the handguard and the piston system makers are in a constant state of flux and the chart would be out of date before this manuscript got to the printers. Instead, contact the handguard and piston makers. Ask if they have handguards that clear their piston systems, and which ones. Contact the piston maker and ask if they have a list of handguards that clear their piston.

BEFORE YOU START

Almost all piston systems require the removal of the entire gas system, including front sight or gas block, handguards and flash hider. I will assume for the purposes of this chapter that you have gotten to this point by means of one of two paths. You have taken your existing DI-system AR and have stripped off everything forward of the delta ring assembly and removed the bolt and carrier assembly out of the interior. Or, you have built the upper receiver and barrel from parts, and are proceeding from there with the piston system.

If you are not yet at that point, then you need to dive back into the book and find the steps you need to get the various parts off before starting the piston installation.

CMMG CONVERSION

Central Missouri Machine Guns (CMMG) have been making ARs for many years now. Their conversion system is a complete set, including gas block, piston system and replacement carrier. Strip your bolt/carrier assembly and install the bolt, cam pin, firing pin, etc. into the new CMMG carrier. CMMG includes a small spring for the bolt tail. Its smaller end goes onto the bolt tail first, before you insert it into the carrier.

The CMMG is a complete gas block with piston and replacement carrier.

If you are going to use regular handguards, slide the CMMG replacement handguard cap on first. Loosen the gas block clamping screws, then slide the piston assembly onto the barrel. At this point you have to make sure the piston is aligned with the clearance slot in the barrel nut. If you are using a flat-top upper, this is easy. CMMG has made the pic rail on top of the gas block the same height as the receiver rail. Place the receiver assembly upside-down on a flat surface, and let the two rails self-align.

Once aligned, tighten the three clamping screws.

Now check fit. Install the bolt/carrier assembly. Push it all the way closed, and move the piston to see if there is clearance when the bolt is closed. When the bolt is closed, the piston should not be touching the thrust shoulder. You want .025 inches of travel. If the piston, at rest, (fully forward) contacts the thrust shoulder, loosen the gas block nuts and move the gas block forward to create the clearance. CMMG says that contact is fine, as long as there is no rearward push by the piston on the carrier when the system is at rest. I’ve found that the easiest way to ensure there is no rearward thrust is to leave the small gap of 0.025 inches.

There is enough overlap in the gas flow channels of the gas block that moving the block a small amount will not restrict gas flow.

Once the piston is aligned, and there is thrust shoulder clearance, tighten the screws, install the handguards, finish building the rifle and head to the range. Test fire to make sure the system works. Once you are sure the rifle works reliably, loosen the gas block screws one at a time, apply Loctite and tighten.

ADAMS ARMS

My Adams conversion has endured heinous abuse, surviving years of range trips, classes and demos. The newest design is actually sleeker than mine, but the approach is the same. Adams uses a bushing to guide the piston, which you’ll have to press into the upper receiver. You must use a standard barrel nut to guide and support the piston.

Then it is a simple task of sliding the gas block on and aligning the piston before you tighten the clamping nuts and screws down.

One advantage of the Adams Arms conversion is the adjustable gas flow. You can dial back the flow for use with suppressors. As an extra bonus, the system’s gas block does not vent gases directly to the atmosphere, reducing sound boost from the vent while you’re trying to quiet your rifle with a suppressor.

The CMMG, like all piston systems, uses a thrust shoulder instead of a gas key.

ARES GXR 35

The Ares GXR 35 is a replacement system that does not require removal of the front sight assembly. Pull the bolt/carrier assembly, strip the parts out and install them in the provided Ares carrier. Take off the handguards, drive out the roll pin and remove the gas tube. Slide the rear of the piston into the gas tube opening in the receiver. Slide the front of the piston system into the front sight, driving the gas tube pin back in place. You’re done.

On mine, I found that I had to file a bit of clearance on the gas tube housing to get it to clear the profile of the barrel. I was installing it in a Rock River Arms carbine, and the barrel was a bit larger right up at the front sight housing. That’s life.

The Ares comes with an upper handguard that has been cut to clear the front of the piston system, but if you wanted to modify any other handguard, the Ares comes very close to not interfering. You won’t have much, if any, material to remove.

A close-up of the Ares.

On this particular barrel, I had to file a relief flat on the Ares to fit it in place.

OSPREY OPS 416

The Osprey conversion likewise doesn’t require removal of the front sight assembly. So if you need a piston system, but want to maintain the mil-spec front sight appearance, you can use the 416 piston. It comes with a replacement carrier, so you can strip your bolt/carrier assembly and install the internals in the new Osprey carrier. Remove at least the upper handguard (both would be better). Drive the gas tube pin out and remove the gas tube. Insert the piston chamber of the Osprey into the front sight housing, using the gas tube roll pin (or replacement) to hold it in place.

Install the op rod into the receiver and push it to the rear. Position the kidney-shaped piston over the op rod, and slide everything forward into the chamber. Press the clip into the piston. Be sure to slip the loop of the clip around the piston. The clip holds them together.

Put your handguard back on and head to the range for testing.

The Osprey 416, with the retaining clip in place and the replacement carrier in front.

The clip that holds the piston rod to the piston.

While the kidney shape of the piston and chamber make it easy to fit under a regular handguard, that very aspect might make it difficult to fit under one of the free float designs. You probably will have better luck with one of the more tubular shaped handguards, rather than the older quad-rail design.

One tip on the Osprey. The piston, the part that clips onto the kidney-shaped assembly, is not symmetric. It has a top and bottom. If it's upside-down, the tip of the clip won't pass through. If it is resisting assembly, check for that.

PISTON CONSIDERATIONS

Piston systems limit you somewhat when it comes to handguards and barrel nuts. Many of the systems use the standard barrel nut — specifically the clearance slots in the flange that provide clearance for the gas tube — as support and guidance for the piston. If your barrel nut is off center, your piston system may be unreliable or even inoperative.

Depending on the particular piston system, you may not be able to use some handguards at all, as they utilize a proprietary barrel nut that doesn’t offer support and guidance to the piston.

And finally, some handguards will not have enough internal clearance for the piston parts. If there’s no room, there’s no room, end of story.

NON-CONVERSIONS

You can buy a ready-to-go piston-equipped rifle from a veritable host of providers. From the early LWRC guns, to the latest Ruger (and who would have seen that coming, even just a few years ago?) you can find one in almost any AR makers’ catalog.

What you have to keep in mind, however, is that they are all proprietary. While any piston-driven upper will fit on any lower (assuming they kept to the specs) the upper internals are not interchangeable. If you break or lose a piston for the XYZ Armory piston system, you cannot simply buy a piston replacement from a supply house. It has to be that particular model from that company. If that firm goes out of business, you’re toast. You’ll have to re-build back to a DI, or convert to some other piston system.

Keep that in mind when you decide to go piston. Now, the chances that Ruger (just to name one) will go out of the AR business or drop the piston gun from their lineup, seems minimal. And even if they do, you can pretty much count on being able to get spare parts for years to come.

But still, it isn’t the bog-standard DI system, where you can find parts anywhere.

CHAPTER 14
COMPETITION TUNING

So you want to compete. You’ve had a bit of experience and found you like it. But you’re starting to think your bone-stock AR is holding you back. That probably isn’t the case. If you have just started, your rifle is the least of your match hindrances. But, we are all interested in winning, and the assumption is the fastest way to victory is to use the same kind of gear as the winners.

It is a common, even firmly held tenet in music that if you are really interested in learning, you should start with the best quality instrument that you can afford (not necessarily the most expensive). Generally speaking, achieving good musicianship out of a poorly made instrument is much more difficult than from a good one. You pony up the cash (or your parents do, since you probably start as a kid) and give it a try. If you succeed, then you’re on your way. If you find out that you have no talent for music, then you can sell the instrument and take up stamp collecting.

While there aren’t many piston guns in competition, such systems do offer tuning settings, mostly for use with suppressors.

A competition tuning system. The long Allen wrench is used to reach under the handguard and adjust the gas flow from the block into the gas tube.

The idea is that a top quality instrument gave you your best chance — if you were hindered at all it wasn’t due to the instrument’s limitations — and the re-sale did not involve too much of a loss (though like anything in the used market it certainly can). This analogy is illustrative for shooting. If you want to get started, a top-dollar rifle won’t necessarily make shooting that much easier, but you’ll also have the confidence that some of the controllable issues in your equipment are covered and aren’t causing hindrance. In shooting, as in music, good teachers focus students on having fun and building skills over time. Eventually, the winning scores and standing ovations from rousing performances follow suit. Moreover, a basic rifle isn’t necessarily holding you back, provided it works with 100 percent reliability. Nothing takes the fun out of shooting faster than malfunctions. On the other hand, there is a case to be made that a difficult-to-play instrument will build up your muscles, hone your coordination and force you to really play through the toughest conditions — increasing the speed at which you learn. Once your skills are sharpened up on that old clunker, your brand new performance-quality rig will be that much easier to play when it comes time to perform.

So don’t be afraid of what you perceive as intermediate-grade equipment. It can turn out to be the best stuff ever on which to learn.

Let’s assume a few things as given, just to make this a bit easier. We’ll assume that your total points were the same as the stage winner. We’ll cover the accuracy part of it along the way, but let’s not make this too complex. Let’s say that you just finished a stage at the club, and your time for the stage was 30 seconds. The Limited or Tactical winner finishes in 20 seconds, and the Open first-place finisher did it in 12 seconds.

The difference in rifle only accounted for about two seconds of the difference in times. That’s right, the Open shooter shot the stage 18 seconds faster than you did, but his/her rifle only made up two of those seconds. The rest of that time was accomplished with faster reloads, quicker transitions between targets and arrays and smoother movements between shooting locations.

The Allen wrench in use. Clearly this is not an on-the-fly change. You want to do this with the rifle unloaded.

However, once you have worked on all those other aspects, and you find that (and we’re just grabbing numbers out of the air) you have your time for that stage down to 24 seconds in Limited or Tactical, and 15-16 in Open, it is time to start building a rifle for the match, and tuning it. Practice and good technique will carve most of the time differential off, but for the last two seconds, you need the best gear.

THE TUNING PROCESS

Start by settling on a barrel length, weight and gas system. Most competition shooters use a mid-weight barrel profile for balance and speed of handling, and a mid-length gas system on an 18-inch barrel. This combination tends to provide softer recoil and good velocity with fast handling. However, if you are shooting bone-stock with iron sights, you may well want a 20-inch barrel if your club provides longer range shots. If you are tall, a 20-inch barrel will not be as much of a hindrance to handle as it will be to a short shooter.

Colt Competition builds an adjustable gas system into their rifles so you can fine-tune gas flow and recoil.

For clubs limited to 100-yard ranges, with the rare 150–200-yard shot, you may be happy with a 16-inch barrel.

The process will be the same, regardless, just some of the details may change as you proceed.

AMMO

To compete, you need two types of ammo, a practice and match load. The only real differences will be the bullets and the brass. For example, your practice load could be one that features gallons of 55-grain FMJ surplus bullets, while your match load should be a 52- or 55-grain high-quality hollow point. The 55 FMJs might only shoot to 2 MOA, while the match bullets shoot sub-MOA, but as long as they have the same point of impact and trajectory the 55s will do for practice. You buy them because they are cheaper. I almost wrote “because they are cheap,” but times have caught up with me. I’ve been doing this long enough that just the projectiles alone now cost more than the full-up cost of the reloaded ammo I created back when I began. You should be jealous, I was loading 55-grain practice ammo back in the day for not much more than $120/thousand rounds. Bullets now cost more than that.

The difference between brass is, your practice ammo will be loaded on used, multiple-fired brass. The match ammo will be loaded on new or once-fired brass. And by “once-fired” I mean fired once by you, in practice, then carefully collected, sorted, cleaned and fully prepped before being reloaded.

POF makes the Dictator, an adjustable gas block with multiple settings.

Load your ammo and develop it so you produce enough velocity to make Major/Minor (power factor in competition), ensuring it’s reliable and accurate in your rifle. No other rifle matters in this regard. If your practice load is 2+MOA, and your match load is sub-MOA in your rifle, but your shooting buddy's gun is 4+MOA with practice ammo, and your match load is 3+MOA, so what? If anything, it is a bonus; he won’t be borrowing ammo from you at a match. What matters is, your ammo has to perform 100 percent of the time in your rifle, and no other (except possibly your backup rifle, if you have one).

Use the practice load to break in your newly built competition rifle. Yes, newly built. You’re probably not going to be tuning like this until you’ve had a season or two of match competition experience. That’s how you know what division you’re going to compete in, what details you need and want, and what aspects of a rifle build matter to you.

If you cannot load reliable, accurate, Major/Minor ammo, there is no point in proceeding with the rifle tuning. The particulars of ammo reloading are not within the purview of this book. If you are having ammo-related problems, you have to sort them out before you go further.

REAR UPGRADES

Look at the buffer weight and spring. If you want to run a more-or-less standard system, swap buffers until you find the heaviest one that still locks open when empty. You can swap in a spring-loaded buffer because you may be tuning the gas system. The tuning on the rear is to deal with the “thump” on the back end, and spring action, if it matters. If you are running a bone-stock rifle (no muzzle brake) then almost all of your tuning will be done back here.

You also have to keep in mind what carrier you are using. If you have elected to use a lightweight one, you don’t want to be undoing that work by dropping in an H3 buffer.

The POF wrench on the Dictator gas block.

FRONT UPGRADES

Gas flow and muzzle brake are the two things that need a tuning on the front of the rifle. Gas flow can be dealt with by either gas port/system changes or adjustable gas blocks. To run an externally stock rifle with a stubborn thump in the back end and excess recoil, install a smaller insert in the gas system. The insert acts as a valve, throttling down the gas flow to the receiver. This is an “install and try” process that you’ll have to do at the range. So haul your rifle, ammo, tools, and anything else you’ll need out to the gun club and set up shop. Pull the front sight assembly off, install the insert to be tested, re-assemble and test fire with match ammo. A round or two will suffice, don’t burn a whole magazine. Keep going down in gas flow until the bolt fails to lock open when empty, and go back up to the next-larger (or two) insert. The result should be gas flow throttled back to the minimum, decreasing or eliminating any bottoming out on the back end.

With the receiver out of the way, note how the gas tube rides over the barrel nut and back into the receiver. If the nut is not aligned, the tube gets shoved at an angle, and that is bad.

The gas flow has to be balanced with the weight of the reciprocating mass in the carrier/buffer combo. The ideal competition system has the least mass pushed by the minimal gas to reduce backend thump, while still delivering sufficient gas to the brake to dampen any remaining felt recoil. This can be a tricky balancing act, and one that can consume more than a couple of range sessions to get just right.

The adjustable systems are easier, but still adjust and try. Set the gas flow to the next lower setting and test fire. Again, continue until the bolt fails to lock open and increase the gas flow a setting or two. An adjustable gas block like the POF Dictator makes the task a lot easier. It has at least nine positions, and the adjustment knob can be turned by the wrench POF supplies, a ³⁄₃₂-inch hex wrench, or a flat-blade screwdriver. The Dictator gives you repeatable settings, but it works like any other adjustable gas block.

You should now have found the minimum amount of gas to run your system with your ammo. Depending on how much operating margin you have built or tuned in, your rifle might be really annoyed if you let it get too dirty. In a dusty environment, it might be prudent to scrub the chamber and add lube between stages. Only practice and match experience will tell you if you have sufficient operating margin in the gas setting. Should you change ammo, you’ll have to do a lot of this testing all over again. If you arrive at a match, but your ammo doesn’t, you may not be able to use borrowed or store bought stuff.

The JP buffer is lightweight and meant for competition only. Use it to decrease felt recoil, at the cost of operational margin.

It is for that reason that some competition shooters do a more detailed and involved build-and-tune process. They settle on a common factory load (let’s just call it Winchester White Box) that’s available everywhere. They find or build a rifle that shoots that ammo accurately and makes Major/Minor. They tune the rifle to run reliably, then load up matching practice ammo. For match use, they use the Winchester so that if their ammo doesn’t arrive they can simply buy it at the nearest store.

The drawbacks to this approach are cost (factory ammo tends to cost more than reloads) and availability. If your ammo fails to arrive at the match, you are now depending on a nearby sporting goods store to have it in large enough quantities to get you through the competition. Not to say anything of the time required to acquire it.

MUZZLE BRAKES

The other thing you can tune for performance is the muzzle brake. Some matches and divisions don’t allow them. Even so, there is some tuning you can do to an A2 flash hider.

As discussed in detail earlier, the muzzle brake works by diverting and redirecting gases. It produces a soft-shooting rifle with minimum gas flow and a decreased back-end thump. For your next step, you will cut on your muzzle brake, which is likely overly effective, working too well for its own good. That is, it probably pushes the sights down off of the target. You want to bore out the clearance hole or holes until it shoots flat — no muzzle rise. You also want to adjust how it sits on the muzzle by adjusting its cant. Depending on your particular shooting stance, the recoil drives the sights to the outside. Right-handed shooters tend to see the sights pushed to the right in recoil.

AVOIDING AMMO WOES

This isn’t a rifle situation, but it is still illustrative. I went to the 2005 IPSC World Shoot, in Ecuador, to compete in the Revolver Division. One quirk of international air travel is the restriction (actually a recommendation, not a hard-and-fast rule, but try explaining that) of being allowed to transport only 5 kilograms of ammunition in your checked luggage. None is allowed in your carry-on, either. I was to travel early, which was good. At the airport, they actually inspected and weighed my ammo, and don’t you know, 600 rounds of .45 ACP weighs more than 5 kilos? (5K is 11 pounds).

I rescheduled my flight for the next day. (I wasn’t going to make the flight anyway, and I wasn’t going to simply stuff the extra ammo in a trash can.) I went online and contacted gun shops in Ecuador near the match, to score some ammo.

I managed to score a small supply of WinClean, non-lead ammo. Once I finally arrived there, I was also able to borrow ammo from an importer I knew. With three sources of ammo I was able to shoot the match. However, the three loads had two different weight bullets, and three different power levels. All shot different zeros. It was a real struggle to juggle the ammo type, trying to match the stage requirements for speed and accuracy.

Would you want to do that in a rifle match, where a change in zero of a couple of inches could cause you to drift your shots into the no-shoot next to the target you are trying to hit? Probably not. Travel with firearms can be a hassle.

When I shot in the World Shoot in Rhodes, Greece, six years later, we all managed to find a way to ship our ammo ahead. Life was good.

By tilting the muzzle brake to the right, you counteract that movement.

Why save all this for the end? Simple. The effectiveness of a comp depends on gas flow. You cannot tune a comp to a setting which will work with any and every load. The burn rate of your match load and barrel length of your rifle determines the volume and pressure of the gas at the muzzle. Only after you have your match and practice load nailed down can you tune your comp/brake. Also, the baffles in the brake determine how much forward push it creates to dampen thump. If you already have much of that taken out of the system by buffer weight/spring and gas flow to the receiver, you don’t want your brake vigorously pushing forward.

If brakes all work the same, why are there so many? Because they don’t all work the same. Some are smoother than others, and this can be a personal thing. Two different brakes may dampen rise and thump equally, but one may have more or less vibration than the other. You can see it once you get to a high level of skill — that's when brake model matters. Until then, it doesn’t.

The end result of proper tuning is a .223/5.56 rifle that literally has no more felt recoil than a .22LR. It will be incredibly loud, even hazardous to stand next to, but it won’t recoil.

The end result of this work will be a rifle with so little felt recoil that you can see the bullet strike on a steel plate … through the scope. Or when shooting long range you can watch the bullet trace as it passes through the air.

A2 TUNING

Short of installing an internal baffle (which some gunsmiths have done, and certain competitions allow) you cannot make an A2 flash hider create forward recoil dampening. However, you can dial in a small amount of muzzle rise dampening.

This requires a bit of work, a fistful of A2 flash hiders (luckily they aren’t expensive) and a machinist who is willing to work with you. Have him bore out the clearance hole for the bullet on the inside of the flash hider, cylindrically and axially to the bore. The design of the A2 (and the A1 before it, but this trick won’t work on A1s) is meant to hide flash. So, the inside front of the A2 is a simple cone, coming back to the rear.

By having your machinist bore it out to a larger, cylindrical dimension, you are creating a thrust surface. You’re not making a bigger cone, but creating a cylindrical “neck” on the inside, at the rear of the A2.

The dimensions matter, but I cannot give you hard-and-fast sizes. The barrel length is a big deal, and the particular powder you use is a smaller variable. A carbine will need a different dimension than a 20-inch rifle. Powder matters only to those with very discerning recoil needs.

Take too much material out and the muzzle gets shoved down. Take too little, and it still rises. Get it right, and the muzzle will stay pretty much on target, even though you don’t have a muzzle brake installed. It will still thump straight back, however.

The big advantage is that for most competitions and rulings it is not considered an external modification. In fact, it isn’t noticeable at all unless someone looks inside your flash hider with a bright light, and knows exactly what a non-modified A2 looks like.

COMPETITION REMINDER

Before you undertake any of this, be crystal clear about what is allowed in the competition and class/division you are entering. What works and is permitted in NRA High Power doesn’t really matter in USPSA multi-gun. In multi-gun if you get a technical detail wrong you get bumped up to the top, or Open Division. Having to compete in Open, because you erred in a minor detail that isn’t allowed in others, is a painful way to learn.

CHAPTER 15
MAGAZINES

Don’t become obsessed with magazines. It was once common to blame a whole host of ills on them. What we found out was that the original aluminum mags were somewhat marginal. But they were more durable than we gave them credit for, and the malfunctions we attributed to them were almost all due to the rifle.

No matter how many magazines you have, mark them. That keeps yours straight from other shooters, and lets you track them in case one becomes unreliable.

Real-deal USGI magazines come in boxes like this. That also means they “disappeared” from government possession.

Some background is important here. Original magazines held 20 rounds, for no other reason than that was believed to be enough ammo. The Army had recently gone from an eight-shot M1 Garand to the M14, which used 20-round magazines; neither Stoner nor Armalite saw any reason to do more than that.

The original and subsequent 20-round aluminum magazines are almost never unreliable, nearly indestructible and still highly valued by many. If you have a reliable AR, and a basket full of USGI 20-round mags in good condition, you are not the least bit disadvantaged.

Okay Industries has been making USGI magazines for almost half a century now. They work.

The 30-round mags came about because we were fighting an enemy who used a rifle with a 30-round capacity and we just couldn’t have that. So, Colt undertook a crash program to develop 30-round magazines. Except they had one problem: they had not been in continuous production of the AR-15. As a result, the mag well dimensions differed, and the best magazine design wouldn’t fit all of them. The best mags produced featured a continuous curve design in which the tube curved smoothly along its length.

The 20-round mags were straight because they really didn’t have to curve. The stack of twenty rounds did not cause enough taper to be a problem. That wasn’t the case with the 30-round ones, however. In response, Colt came along with a straight-curve design in which the top half is straight, like the 20s. Meanwhile, the bottom was curved to accommodate the taper of the cartridges when stacked.

And we’ve been stuck with it ever since.

On the right, the original, black plastic follower. On the left, the “christmas tree” rebuild kit; green follower and red-dyed spring.

There’s another detail between 20- and 30-round mags. The feed lips of the 20s are curved up, but not folded and welded at the back. The spring strength necessary to lift 30 rounds was too much for the free-standing mag lips. Colt had to fold and weld the backends to give them more strength.

The early 30s had problems, too. Since they were hurried into use, and not updated when war ended, we were stuck with relatively weak springs and followers that tended to tilt.

Magpul got their start with magazine baseplates. These Ranger Plates make it easier to get your mags out of a pouch and protect the bottoms from the ground.

As the rifle cycled, the rounds rattled inside the magazine. They would jostle around, and even get out of alignment. The spring, and the follower pressing on the stack, kept things under control. We found that if the follower had too much room to move, it could cause problems. This lead to various designs of what became known as the “anti-tilt” follower. Old magazines could be improved by installing this follower.

But there isn’t much point in doing so, unless you have a footlocker full of legacy mags, ones made literally decades ago. Any magazine you buy today will use an anti-tilt follower. And if you want to replace the follower and spring (springs are much better today than back then, too, there’s no point in halfway measures) a replacement kit costs you $4 each, less if you buy in bulk. You can purchase a complete magazine from Brownells (also the source of the rebuild kit) for $14, less if you buy in bulk. That’s essentially $10 for a brand new tube, made to tighter specs and better material.

Also, don’t bother with any kind of feed lip tuning tool. I love the guys at Brownells like they were my brothers and sisters, but this is one tool you don’t need. All you can do with it is waste time frustrating yourself, waste ammo testing “tuned” magazines, and question your ability to fix things.

Buy good magazines, don’t regret the cost. Should they break or malfunction, destroy them so you can’t mix them up.

Okay makes USGI magazines with a black Teflon coating, which is not USGI. Aluminum is easy and anodizing is versatile. The camo mag is an Okay that got sent off to be anodized in a camo pattern.

ANTI-TILT GAMES

Once the anti-tilt follower had been perfected, the government suddenly took an interest in improving magazines. They changed the color, moved the follower lifter from one side of the centerline to the other, declared it “new, improved, government-designed,” and started production. The designers were not able to make a claim, and that was that. If you hear about the “new government anti-tilt follower” you know it is nothing new, and is more re-inventing-the-wheel nonsense.

CHOOSING MAGAZINES

In some jurisdictions you may have to settle for 10 shots, but for most of us the choice is between 20 or 30. That is a chapter-length discussion that is beyond the scope of this book, so I’ll leave it for later. However, here is a look at the best mag options available today.

USGI

There’s nothing wrong with modern USGI aluminum magazines. Some claim they aren’t durable, but compared to what? Magazines are not intended to survive being run over by vehicles. That they do so is a bonus. There are two companies I would be happy to go to for aluminum USGI magazines — Brownells and SureFeed.

BROWNELLS

Brownells actually makes magazines and they are USGI. In fact, Brownells has filled government contracts with those mags. They have to supply the government with the tan anti-tilt followers, and can’t send those to you. But that’s not a problem, as they will send you the civilian equivalent, with the original perfected anti-tilt follower and you’ll be plenty happy. They make them in various capacities, so you can use them for practice, defense or hunting.

When Brownells decided that magazines were a lucrative commodity, and that people simply couldn’t buy enough of them, they found a local stamping company that had the capacity. They invested in the tooling to do it right, met the mil-specs and, in the usual Brownells fashion, exceeded them. When I last visited, Brownells had coils of 6061 aluminum on the warehouse floor, ready to be trucked down the road and turned into mags.

SUREFEED

SureFeed is the corporate name for Okay Industries, the company that has been making magazines since the Vietnam War. They were involved in designing the 30-round mag from the start, and did a darn good job of it. I was happy with the ones they made back then, and the new ones are even better. Unlike the government, Okay wasn’t happy with the specs, so they spent their own time and effort to improve it, while not straying from the specs the government insisted on. So you have a much better magazine that is in every regard up to military specs. They, too, make them in various capacities, 10, 20 and 30 rounds, but they do not offer any caliber other than .223/5.56.

Okay marks their magazines with the firm’s name, but also the date of manufacture. If you live in a state with magazine restrictions you’ll want to know that.

With a large enough order (or pay the setup charge) you can even have your magazines custom laser-marked. As if that isn’t enough, AR-15 magazines are a relatively new product for them. An earlier iteration of the company made M1 carbine mags during World War II.

MAGPUL

Magpul is the original, reliable polymer magazine for the AR. I remember the first one I ever saw. I was watching Drake Clark of Magpul, all 6-foot 5-inches of him, stomping a magazine with jump boots on. It survived (I have that magazine) and that was that. They have since gone through a raft of upgrades, and you can tell when yours was made because they mold the month and year of production on the side. If you have a question, you can ask them, and they’ll tell you if there have been any problems with that batch.

20-round magazines have curved lips. 30-round magazines have curved lips that are welded on the back, because they need the extra strength.

The big trick with polymer is, you can make the exterior straight or curved, while the interior is a continuous curve.

Magpul magazines come with a clip-on storage cover. It not only keeps dust and gunk out of the mag, but when loaded compresses the cartridge stack, taking the stress off the feed lips. The clip can be stripped off easily when you need it, so you can keep your magazines loaded. It keeps the feed lips unstressed and still accessible.

CCW makes a Magpul coupler that lets you double capacity, although it does make for a ridiculously long magazine.

You can get them in colors, since the polymer takes dyes well. They even have one with a nifty observation window on the side, to see capacity and supply.

LANCER

Lancer took a different approach. They kept the metal feed lips (in their case, they use steel, always a good choice) and molded the magazine tube out of polymer, which is bonded to the steel feed lips in the molding process. It’s not glued; the polymer is actually cast molded to the steel in mold fixtures.

Taran Tactical makes an easy-to-grasp magazine extender that adds a useful amount of extra firepower, but isn’t excessively long.

The result allows them to take some steps that other magazines manufacturers cannot. For instance, if you make the entire mag out of polymer, you can’t go with a translucent mixture, as it will lack strength. But since Lancer uses steel in the feed lips, a translucent body is plenty strong. And they can mix in other, more subdued colors.

Clear, translucent/smoke, green, brown, 5, 10, 20 and 30 rounds, Lancer makes mags for all applications. But they only make them for .223/5.56 and .308/7.62 NATO, with one exception — a 7.62x40 specific mag made specifically for Wilson. If you have a Wilson Combat rifle in 7.62x40, or have built one, you should source your magazines to fit.

How tough are magazines? This one is being run over by a small SUV. It worked just fine afterward.

MISSION FIRST TACTICAL

Mission First Tactical (MFT) is a newer company offering mags, but they jumped in with full enthusiasm. MFT offers polymer magazines with all the options you could want. That includes anti-tilt follower, stainless steel spring, a floorplate that can be marked with a paint pen to number, and textured non-slip panels on the mag tube.

They also offer replacement baseplates, color coded in red, orange, yellow and green. You can use them to keep track of what ammo is in which mag (M855 “green tip” in the green baseplate mags, for instance) or to indicate which are your training and practice mags.

BASEPLATES

Which leads me to the subject of baseplates and replacements. Magazines in tight mag pouches do not fall out. They can be tough to get out when you need them. Back in the prehistoric days we used “ranger cord” to make life easier. We’d take a 4-inch length of 550 cord, tie a knot at the ends and burn them to prevent fraying. Then we’d lay the cord on either side of a USGI mag in the “gutter” and wrap green 100 mph tape around it. The cord now becomes a loop.

Well, one of the first things Magpul made were replacement baseplates that had built-in loops or extended bases for grabbing.

Another approach is to use an extended baseplate, like the ones available from Taran Butler and Taran Tactical that give you a good handle to grab (and add capacity).

Magazines can be rested on the ground, it won’t cause a malfunction.

If you really want to increase capacity, get a California Competition Works mag coupler. It connects two Magpul magazines, base to base, which doubles capacity. I’d use a bit more 100 mph tape to secure the bottom retainer, but that’s me. Remember, when you are planning to use it in a match it is twice as long, so you won’t be able to go prone.

MAGAZINE MYTHS

Resting the magazine on the ground while you are shooting won’t cause a malfunction. We’ve tested this extensively in classes, and unless the ground upon which you are resting is pure sand, or a swamp, using the magazine as a monopod isn’t a problem.

Second, you don’t make a magazine better by disassembling it and stretching the spring. In fact, just the opposite. Stretching it past its design limits work-hardens and weakens it. If the mag is unreliable, try a new spring. If it still doesn’t work, install a new follower. If that doesn’t do the trick, pull the new parts back out and scrap the rest.

The best part about the GTul magazine cleaning brush is you don’t have to take the magazine apart to brush it out.

CARE AND FEEDING OF MAGAZINES

To care for your mags, hose the mud off. Occasionally take them apart and let the crud fall out. You can brush them clean if you want, GTul makes a brush for that. Magazines are tougher than we give them credit for, and you will find that even stomping on them or running them over with a car won’t cause breakage.

It is prudent to mark them. Use a paint pen to put initials and numbers on each. You can use a stencil, but the paint pen is a lot more convenient.

SERVICE LIFE

Nothing lasts forever. When your AR magazine reaches the end of its service life, do not mourn it. Don’t be cheap and try to resurrect it. If the tube is cracked or mangled, or the feed lips are awry, ditch it. Save the spring, follower and baseplate for spare parts.

CHAPTER 16
TOOLS

In a combat setting, the only two things you can always count on the troops having are rifles and ammunition. As a result, the AR-15/M-16 was designed, as all good military small arms are, to be taken apart with either the bare hands or with the assistance of a loaded cartridge.

However, any repair or maintenance more involved than field-stripping requires proper tools. A soldier can take his rifle apart with his bare hands, but he can’t clean the bore nor scrape the carbon off the bolt. This is where a more advanced toolkit becomes necessary. There are a large number of specialized tools for the AR. Not because working on the AR-15 or M-16 always requires such tools, but because having a specific tool can make a difficult job easy.

The Otis kit is a field kit, not a bench kit.

A cartridge should not be used for disassembly, except in an emergency, for it is hard on the cartridge. Having loose, live ammo present when performing maintenance or cleaning is asking for trouble. Ammunition should not be treated so casually.

In addition to the basic toolkit, you’ll want a cleaning rod (one-piece is better than a section rod) patches, brushes, solvents and lubricants.

A complete armorer’s tool kit is available from Brownells, in a nearly-unbreakable container that can be carried as luggage or shipped. However, at $1,200 it is more than you may need or can justify.

Brownells makes the ultimate AR toolkit.

BASIC TOOLS LIST

Punch, ¹⁄₁₆ inch Charging handle, Forward assist pawl, A1 & A2 windage drum

Punch, ⁵⁄₆₄ inch Gas tube retaining pin

Punch, ³⁄₃₂ inch A2 elevation spring pin, Forward assist assembly, Front takedown pin assembly, auto-sear

Punch, ¹⁄₈ inch Trigger guard roll pin, Hammer & trigger pins

Punch, ¹⁄₄ inch General pin driving

Taper pin starter Barrel taper pins

Pivot pin install tool Front pivot pin

M4 stock wrench Tele stock castle nut

Bolt catch pin punch Bolt catch pin

Allen wrenches ³⁄₁₆ and,⁵⁄₃₂ inches Pistol grip screws, Allen head type

Brownells front sight block

Brownells bolt disassembly fixture

Extra tools that can be very handy, or are must-haves for certain tasks, and their Brownells part number;

702-003-015 Peace River action block

702-004-015 Lower receiver vise block

080-000-252 Front sight bench block

With a T-handle on a chamber brush, you can keep a rifle going even after it is so disgustingly grubby you won’t want to touch it.

795-015-100 Barrel vise jaws

531-460-000 Snap ring pliers

769-100-223 Broken shell extractor

080-000-079 A2 rear sight spring tool

851-115-001 Bbl nut wrench

939-000-003 Bolt ejector tool

513-100-240 Headspace gauge, GO, 223

513-100-241 Headspace gauge, NO-GO

The Brown tool is the best for scraping crud out of the carrier once you have removed the bolt.

A few tools from M-Guns that you may need are the MOACKS, the 223/556 Gauge, and the 5.56 leade reamer.

Unless something is an emergency, you can acquire the tools you need when you need them. If you are not ever going to replace a barrel, you don’t need tools for that. But if you are going to be responsible for the telestock assemblies of several ARs, you’ll need a good wrench.

Don’t go broke buying things that may be useful someday. As individual tools they aren’t very costly, but it does add up.

With a few basic tools you can get pretty much every part off of an AR — at least all the parts that might need cleaning or replacement.

CHAPTER 17
CLEANING AND LUBE

The AR is a lot more forgiving than many give it credit. I can dunk an AR in water, freeze it in a snowbank, bury it in dirt and run it over with trucks. It's not a fragile little snowflake that needs TLC and kid gloves.

ARs do need some cleaning, and they must be lubed. Anyone who suggests the AR was designed to be used bone dry does not know of what they speak.

Classic Hoppes. Cleaner and lube. Been doing it since forever. Get some.

CLEANING

During training or competition you won’t have time to completely tear down and scrub a gun, so you’ll need field-expedient tools to keep your AR running. The basics are a chamber brush on a T-handle, a Bore Snake and a bottle of lubricant. When the rifle gets crusty and dry, lube it up. First double check that the rifle is unloaded. Apply a drop of lube in each of the carrier vent holes. Draw the bolt back partially, until the extractor and lugs are exposed through the ejector opening. Apply lube to the extractor and at the base of the bolt.

During a lunch break, unload and separate the upper and lower. Pull the bolt/carrier assembly out and lube in the same locations.

Use the chamber brush in the chamber. Push the brush in while turning clockwise, and keep turning as it bottoms out. Pull the brush out while still turning. This will bend the brush’s bristles instead of breaking them. Drop your Bore Snake down the bore and pull it through. This scrubs out the debris that you loosened in the chamber, falling into the bore.

Wipe the bolt and carrier free of carbon crud with a cloth or paper towel, apply some more lube and reassemble. All this takes five minutes and your rifle will be ready to go for many more rounds.

The Otis kit includes a rod guide and can be used to clean the locking lug area.

If you have more time, follow the process I used up at Second Chance. There, we really poured ammo through rifles — making them hot and dirty. I’d take the smoking-hot rifle off the line, open it up and run a solvent-wet patch down the bore. Then I’d set it aside to cool. Next I’d scrub the bolt and carrier, usually with a spray of lube, then a wipe down followed by an aerosol degrease. I’d strip it, scrape the hard carbon off, lube and reassemble. By then the bore needed attention, so I’d run a patch down it to clean out the solvent. Lastly, it was time to scrub the chamber as above, and re-patch the bore with solvent.

In the meantime, I’d load more magazines. When my name was called to shoot, I’d use the rifle next up in rotation (at the peak, I had three rifles I was rotating through) and let the others sit.

When it comes to lube, use what you have, what works and what makes you happy. Just use enough of it.

Finally, I’d wet-patch the bore again, to get the chamber crud out. Then push through a couple of patches, reassemble, and rack it for next in line use.

LOWER CLEANING

There are only two ways to clean your lower. One is to hose the interior with an aerosol cleaner and, once dry, apply lube. Hoppes makes an aerosol cleaner that is meant for just that task. The other way is a detailed strip and scrub with brushes. There is nothing to be gained by trying to go halfway. If you try to brush the interior without removing the parts, you will simply get brush bristles tangled and torn off inside, and have to take it apart anyway.

In the police classes, where we are not doing a lot of really hard work, or subjecting the rifles to environmental abuse, I simply aerosol clean now and then.

On the other hand, during a hard-use class where you may be crawling through brush, dirt or sand, out in the rain, or in blowing wind with dust, I do a teardown and scrub each night that I’m indoors. If I’m not indoors, I do what I can. But I won’t risk losing a small part in the brush or grass, just to try and get a minor amount of carbon out of the lower.

As for the buffer and spring, unless I’ve taken a dunk in a lake, river or swamp, I’m leaving them in the buffer tube until I get home. Nothing good can come from pulling them out in the field or during a class.

BOLT AND CARRIER

For regular use, the above described methods are all I do with my rifles until I get home. Only then will they be subjected to a more thorough cleaning as follows.

The backend of the CRT-15 tool cleans the carrier.

Pull the bolt from the carrier and scrub the carbon off. The tail of the bolt always accumulates a scale of carbon, requiring a dedicated tool for removal. We used to make cleaning tools by mangling empty .50 BMG cases, but they are hard to come by, and the dedicated tools do better. The M4 CAT tool, or the CRT-15 scrape the carbon off the tail of the bolt with ease. The Otis Bone tool not only cleans the tail of the bolt, but scours the inside of the carrier as well.

The front of the CRT-15 tool is adjustable and cleans the bolt tail.

Unless the face of the bolt is flash-coated with brass shavings, I don’t bother to remove the extractor or ejector. Just scrub with solvent and a brush. Remove brass shavings from the bolt by taking the extractor and ejector out and scrubbing. Be sure to look for the cause of the shavings.

Scrub the outside of the carrier and use a bore hole reaming/scraping tool for the interior. Wipe the firing, cam and cotter pins clean.

Put everything back together and lube them up. Apply a drop of oil in the joint of the ejector, pumping it in and out a few times to let the oil work in. Run oil around the gap of the extractor and on the rotating band. That’s the one that is worn white from rubbing. Oil the gas rings and the tail of the bolt.

The CRT-15 works, even if it is a bit larger than the rest.

Be sure to oil the cam and firing pins when installing the bolt. Apply oil to the riding ribs of the carrier. And then set aside.

The Bone Tool from Otis is so compact you can carry it in a pocket.

CHAMBER AND BORE

The chamber gets the same brush treatment as before. For the bore, run a wet patch down, followed by a bristle brush and let it sit for a few minutes. Take a couple passes with dry patches. Repeat until the dry patches come out reasonably clean. Don’t go crazy here, scrubbing, swabbing and scrubbing some more until the last dry patch comes out looking like it never went down a bore.

As long as you keep the bore reasonably clean and free of fouling, you will be garnering most of your barrel’s accuracy. And since barrels fed with good ammo are far more accurate than the shooters using them, the limiting factor is still you.

One tool you must have to do a proper job of cleaning is a chamber brush on a T-handle.

With the barrel out of the receiver for demonstration purposes, note how the chamber brush cleans the locking lugs as well as the chamber area.

That being said, Iosso makes a kit that has a T-handle for scrubbing the chamber, plus bore and upper receiver brushes, all made of plastic — no brass bristles to break off. It also has a special brush for cleaning the gas tube, something that will bring a glow to someone’s heart, I’m sure. Otis makes several good kits, too. One in particular has a guide tube and special locking lug cleaning tools. The kit includes a gizmo that helps you clean the gaps in the gas tube clearance hole in the receiver, but that’s too OCD for me. However, if your supervisor or training Sergeant is a stickler for clean, that might get you some brownie points.

The chamber brush extends past the chamber, through the neck and into the leade of the bore. All this to make sure it is clean.

Otis makes a compact kit that almost fits into a pocket, and certainly is no big deal to add to a rucksack.

THE REST OF THE RIFLE

As long as it isn’t caked with mud, or dripping with slime, I’m not too concerned about the exterior of my AR. Obsessing over the cosmetics and detailing my rifle after every range session just isn’t in my nature. I’d rather spend that time loading more ammo.

LUBRICATION

There are tons of good lube options out there. Ned Christiansen once remarked to me that, “In a pinch, I guess even sunscreen would work.” He then went looking for the nearest non-gun non-lube. He came up with a squeeze bottle of Parkay. After cleaning and lubing a rifle with the foodstuff, he proceeded to shoot an afternoon’s worth of drills. The rifle worked just fine, although the smell was … interesting.

The mistake he made was in not cleaning it out after he was done. When he did, sometime later, the Parkay was so caked on he had to boil the parts to get the stuff off.

Actually, any gun or motor oil will do. Apply it where you need it, and as much as you need, and do not let your AR run dry. You don’t need so much that your shots splatter the shooter next to you, but you do want to keep the carbon build-up as a gooey mess that can be wiped or scraped off. Hoppes has been making lube for a century or more now, and they know the job.

SERVICE LIFE

While the various parts on the AR are not exactly expendable, they are consumable. I’ve even heard of magazines being described as expendable, but they’re consumables. Every part has a useful service life, at the end of which it needs to be replaced. They should be inspected and replaced when they've reached the useful end of service.

Losso makes a kit with all plastic brushes so they won’t break or leave brass scratches on your aluminum.

For a bolt used in an SBR, that might be 7,500 rounds. On a full-sized rifle never subjected to max-pressure ammo, it might be 20,000 rounds. Barrel life ranges anywhere from 5,000 to 15,000 rounds, depending on use and expectations. A High Master at Camp Perry is going to be done with the accuracy a barrel delivers long before a club-level IPSC 3-gunner will be.

Inspect and replace. Keep lubed. Build your skills. Stop obsessing over white-glove levels of cleanliness and keep practicing.

An Otis kit compact enough to fit in a cargo pocket and disappear into a rucksack.

CHAPTER 18
9MM AND .22LR

Colt makes 9mm carbines. They do it by pinning in blocks to fill the mag well. This particular one is a rare select-fire, and in a collection.

The noise generated by shooting a centerfire rifle indoors can make the experience kind of unpleasant. Not all indoor ranges are up to the task of dealing with .223/5.56. New shooters are also sometimes not happy with the noise and recoil of the .223. The 9mm might have the same recoil, but it has less noise. And the lowly .22LR? Noise and recoil free. A 9mm or .22LR make good sense in certain situations. Building one is pretty easy.

9MM

You’ll need a 9mm barrel and bolt, a conversion block for the magazine well (or a Rock River 9mm-specific lower) and a replacement buffer weight.

The 9mm barrel replaces the .223. The backend of the barrel is the same external size and shape, and the barrel nut is the same. However, since the 9mm is a blowback design, you won’t need the gas tube. You will see the stub of a gas tube on some of them, still attached to the front sight housing. It is there to keep the handguards from rotating and prevent the barrel nut from unscrewing. Yep, seen it happen. And since there is no need for a gas tube, the key on top of the carrier is there solely to keep the bolt correctly oriented. That’s why it is cut back on a slant.

The dedicated Rock River 9mm lower. The magazine well has been broached for the 9mm mag and no other. Here is one next to a standard 5.56, and you can see the difference.

Left to right; a .22LR magazine, a Colt/modified Uzi and an aftermarket 9mm mag.

The .22LR is the same size as a 5.56 mag, but the internals only hold a .22 long rifle cartridge. Or, a stack of them. The 9mm magazines are steel, and hold 10, 20, 25 or 32 rounds of 9mm.

Since the 9mm is a blowback design, there is no need for locking lugs. That makes the difference readily apparent on the chamber end.

Install the stock (most shooters opt for a telestock, which makes things easy) and lower internals just as you would any other build. The conversion block comes in two types: one inserted from beneath and held in place by the mag catch, the other from the top, held in by lips that keep it from falling out. Opt for the top-loading one.

Colt uses a pair of blocks pinned into the mag well. If you get a conversion set of parts like this, free or cheap, go for it. Make the top decks of the adapter blocks even with the top of the lower receiver, press hard forward and aft, and drill and pin. Otherwise, go for a 9mm-specific lower (Rock River makes one) or the blocks inserted from the top.

9mm barrels are 36 threads per inch, unlike the 5.56 at 28 per inch. This keeps you from installing the wrong flash hider.

The barrel is installed like any other. Just keep in mind the need to secure the handguards or the barrel nut. A free-float handguard would be very good here.

The 9mm needs the heaviest buffer weight you can get. The H3 will work, if you can’t get a 9mm-specific Colt one. The 9mm uses the same buffer spring as any other carbine.

As mentioned, the bolt is a blowback type and machined without locking lugs. In fact, the carrier is the bolt — it is all one piece.

Last, you may find that some hammers are less forgiving of the 9mm bolt/carrier. If you use a standard .223/5.56 lower internals set, you may find the hammer is the problem. Swap it for a lightened, match-type one and things will work better.

The bore size means you need a larger diameter barrel for the 9mm to maintain strength.

The 9mm barrel has different threads at the muzzle than the ./223/5.56. The thread pitch there is ¹⁄₂-36, instead of ¹⁄₂-28. This is to prevent you from installing an undersized flash hider on your 9mm barrel. However, the ¹⁄₂-36 threads can cause headaches when you go to mount a suppressor. A handgun 9mm suppressor will have threads of ¹⁄₂-28, but that won’t work on your 9mm carbine.

That’s not a problem since the handgun suppressor mount features a booster, which the carbine doesn’t need. So, your suppressor needs a rear cap that is threaded ¹⁄₂-36. The 9mm bore explains why the handgun caliber barrel profiles tend to be heavier. Even at their thinnest, 9mm barrels are larger in diameter than 5.56.

9mm AR magazines are modified Uzi mags. Back in the old days we had the choice of a mondo-expensive Colt mag, or a dirt-cheap Uzi mag, requiring machining with an end mill. Now, there are plenty of 9mm magazines to be had, no need to go cutting on any.

.22LR

A rimfire conversion involves only the upper, unless you find that the hammer is too heavy, a problem solved with a lightened match hammer. Also, the rimfire conversion does not need any specific buffer weight, as the .22LR doesn’t generate enough recoil to push the buffer.

But you will need a buffer and spring installed, to keep the rimfire adapter in place.

The .22LR conversion is a self-contained unit, with its own recoil spring. It needs a buffer and spring only to keep it in place.

The 9mm bolt is the carrier, and vice-versa. There is no need for a gas key, cam pin or separate bolt.

Note how much deeper into the receiver the barrel of the .22LR protrudes. This makes a dedicated .22LR much shorter than a regular 16-inch carbine, even with a 16-inch .22LR barrel installed.

The conversion is a bolt with built-in recoil springs and a forward part that looks like a .223 cartridge, lacking a bullet. That part fills the chamber of a .223/5.56 barrel.

This works kinda-sorta OK. The bullet of the .22LR is made to fit a barrel with a nominal .221-inch diameter in the grooves, while a .223/5.56 is designed for a bore of .224 inches. That isn’t much of a problem, though the same can't be said of the barrel twist. A ¹⁄₁₂ barrel won’t be too bad, but a chrome-plated, ¹⁄₇ twist will be a roll the dice situation. Sometimes it works, and sometimes it is a disaster.

The better solution is to use a .22LR-specific barrel. You can get these (and the conversion kits) from CMMG, among others. I’ve used the CMMG, so I can say from experience it works. Since the .22LR does not need the .223-shaped extension, and is a blowback design, the .22LR barrel protrudes into the receiver farther than the .223 barrel.

As a result, a .22LR dedicated AR has an overall length closer to that of an M4 with a 14.5-inch barrel than a 16-inch carbine. It will be, generally, an inch and a quarter shorter overall than a regular carbine. But the rimfire still has a barrel 16-inches plus in length. If that makes a difference in the overall length (You never know, local and State law can be quite irrational) then you need to know before you build.

Barrel threads are normal ¹⁄₂-28 and regular rimfire suppressors will screw right on. Also, centerfire ones will too, but that’s asking for trouble. Rimfire runs dirty, grubby and ugly, quickly loading up your centerfire suppressor with powder residue and lead, making it less efficient and heavier.

As with the 9mm, the barrel nut is not locked in place by the gas tube (there isn’t one) so you will have to go to extra lengths to make sure it stays tight.

AR-style .22LR magazines are shells of centerfire size, with a spring and follower inside to accommodate the little rimfire cartridges. They use the same mag catch as the centerfire.

You can build a complete upper or a dedicated rifle. To swap for a dedicated upper, remove the centerfire one, put on the rimfire and slap in the rimfire magazines. Done.

THE FUNNY PLASTIC THING

There is a plastic lump at the back of the shortened ejection port cover. You don’t really need it. Colt does that because they are locked into the slickside uppers for 9mm, and need it to deflect gas and brass. If you are using an upper with a built-in ejector lump, you can go with a standard door.

CHAPTER 19
ASSEMBLY TIPS

Two questions come up in every AR armorer’s class. One is, “What is the best AR?” and the other, “In what order do you assemble a box of parts?” No, really. I get questions like this all the time.

Let’s take the second one first, how to assemble an AR from a box o’ parts.

First pull everything out of your box o’ parts and do an inventory. Some parts may be missing, duplicated, wrong or even unidentifiable. You want to make sure everything you need is at the ready before you start.

Dabs of paint, at strategic locations, can tell you if the fasteners on your rifle have come loose.

Next, do a preliminary inspection of the parts, making sure they are the correct ones. For instance, if you ordered a barrel with a ¹⁄₇ twist, is it marked to reflect that? If not, you have a return or exchange to make. Similarly, if you ordered a barrel with a mid-length gas system, and the gas tube that arrived with it is a carbine or rifle tube, you need to make a swap. Do you have the correct buffer for the stock? Is it the correct stock?

Once you've made sure that all the parts are there, and they are the ones you asked for, you’re ready to check fit.

AR ASSEMBLY PROCEDURE

Start with the upper, lower and the two takedown pins. Press the upper and lower together, passing the front pin through. Don’t worry about the retainer or spring, just fit the pin. Check that the upper hinges smoothly on the lower. If not, you’ll need to swap parts until you find ones that do. Close the upper and lower, pressing the rear pin through. It should slide in smoothly. The upper and lower should have little or no wobble.

If you can’t fit the pin in, or it needs to be pressed or hammered, pass on this set and have the place you got it from replace one or both.

No matter where I go with an AR, I take a chamber brush on a T-handle with me. You never know.

Here’s a pro tip. If you have other rifles, go on a fit-check mission to see if your other uppers and lowers will match with the new ones. If you’re willing to do some swapping, you can often find a set that will work.

If all of your parts came from a genuine mil-spec shop, and they don’t fit, you have cause to complain. But the volume of good non-mil-spec products is large. The number of real-deal mil-spec parts is a small subset. You can build a perfectly good AR and not have a single mil-spec part in it. That’s your choice.

Check how well the other major parts match. Does the barrel extension slide smoothly into the upper receiver? Is it excessively loose, or does it fit so darn tight you’ll need a mallet? Does the buffer tube screw into its hoop on the lower, or not? Is the handguard the one you asked for, and will it fit the barrel length? If it is supposed to come with a replacement barrel nut, does it?

UPPER AND LOWER ASSEMBLY

It doesn’t matter if you start assembling the upper or lower. I tossed a coin, and tails came up. So I took that as a sign that I should describe the sequence of assembling a lower first.

LOWER

Check the fit of the fire control parts in the lower. Do they fit? Do the pins go through? Is the trigger pull something approaching normal? If so, pull them out. Check the fit of a magazine to the lower. Does it slide in normally and fall out of its own weight? Good, then we can go on.

In sequence: Install the bolt hold-open, trigger guard, front takedown pin, fire control parts, pistol grip and then the stock. Since it doesn’t have to depend on anything else, you can install the magazine catch any time that suits you. If there are any extra parts or accessories you want to put on the lower, add them last, unless they have a reason otherwise. One example would be the single-point sling plates on buffer tubes. If you are going to use one, install it as part of your stock assembly. Don’t install a plain one only to remove it and replace with a single-point.

UPPER

Begin with the bolt and carrier. Check the carrier for a properly staked key. If wrong, get it staked. Assemble the bolt, with all of its upgrades (read about them in Chapter 5) and do the function checks. Install the forward assist, if any, and the ejection port cover. Install the barrel, gas or piston system, flash hider or muzzle device, handguards, sights and optics, and then put the upper and lower together.

Once parts are tight, and have stayed tight after testing, they get painted-in.

There, that wasn’t so hard, was it?

Truth is, I had to figure this out from scratch back when Reagan was President. I made mistakes, but then I moved on, and here I am. So, if you make minor mistakes non-essential to function while assembling your rifle, it isn’t the end of the world. Look on it as a learning experience, and make the next one better.

THE VERY BEST ARS

What is the best AR? That depends on what you want, need or desire. A SWAT cop going on a raid will be vastly comforted with an SBR, an 11.5-inch telestock carbine and a red dot sight. A suppressor would be heaven. A varmint shooter would not look at that SBR with much enthusiasm. The red dot optic would be inadequate for his needs and the suppressor would be superfluous.

What matters is, does it work? To make sure an AR works, I have a process, a set of tasks that I check and correct if needed.

First, I make sure everything is tight. Then I do a quick dry function check, making sure the safety, trigger, disconnector and hold-open work. I check that magazines fall free of their own weight. (If not, the rifle goes back, as that is not an easy fix.)

What’s the best AR? The one I have checked, inspected, tested, zeroed and painted-in. Then it is the best.

If everything checks out, then I begin the inspections that might require mods. If I start wrenching or banging on a new rifle, and then have to send it back, the manufacturer is understandably going to be a bit leery. I might even shoot a new rifle a bit before I make any changes at all, just in case it has a hidden function problem. But once I get to the point that I’m going to keep it, and correct it if needed, I check the following from back to front: castle nut, buffer weight, gas key, leade.

Castle nuts must be staked. I check the tube to make sure it has a good hold on the buffer retainer and then stake if needed. For carbines, run the heaviest buffer the gun will reliably work with, using the softest ammo it can be fed. Do some swap-and-try range work or, if it feels a bit harsh in recoil, jump right to an H3.

The gas key must be tight and staked. If it isn’t, it gets tightened (or removed, cleaned, hosed and tightened. Again, see Chapter 5) and then goes through the MOACKS.

And then finally, it must have a 5.56 leade. Measure it with the .223/5.56 Gage from Ned Christiansen (www.m-guns.com) and ream the leade if needed (I also recommend Christiansen’s reamer for this job).

Add sling, scope or other accessories as needed to fulfill the niche for which the rifle is being built. Lastly, test fire, establish a zero and make sure it works properly with its assigned magazines. Do the testing with the ammo you expected the rifle to shoot later on, based on application. Paint in the various attachments, settings and parts that need to stay tightly attached. That way, if they loosen, shift or otherwise try to break, you’ll have visible evidence of the change.

Then, and only then, is it the best AR.

PAINTING IN PARTS

Just how do you do this “painting-in” thing to which I refer? It starts with a paint pen. When I started this, my local hardware store had Krylon paint pens and that’s what I used. I’ve always been happy with them, but in doing some recent research I found that there are a lot of others. It seems that pretty much anyone who makes paint, offers a pen applicator for it.

With that in mind, my process is as follows:

Ensure that the part to be secured is tight and has been test fired. There’s no point in painting until you’re certain everything is as it should be. Once you’re sure, then you’ll need a degreaser, the paint pen and your usual lubricant.

Use the aerosol degreaser or a cotton swab with rubbing alcohol to degrease the area on and around the place to be marked. Take the cap off the paint pen, shaking it to get the paint mixed. Take a few test dabs on a smooth surface that you can clean or toss. Once the paint is flowing, and you have a feel for how much comes out on each press, you can begin.

Apply at the overlap of the screw heads and nuts by pressing the paint pen in once and releasing. That’s it. You want a circle or oval of paint, not your signature. The paint will wick into the gap between the nut and surface or the head and surface recess. It will be a visible circle, and if the screw or nut moves, the circle will be broken or misaligned.

That’s it, the job is done. Lubricate the area only after the paint has fully dried. Color is up to you. If orange or hot pink does the trick, go for it. If you want to be “tactical,” (whatever that means) then select something that is still visible to check, but won’t be inappropriate for your setting or social group.

Paint is a simple thing. But sometimes the simple things can make a big difference.

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ISBN-13: 978-1-4402-4660-9

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TABLE

Source | Go | No-go | Field | Colt factory reject/aka Field II
SAAMI | 1.4636" | 1.4666" | 1.4696" | 1.4736"
USGI | 1.4646" | 1.4706" | 1.4730"

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