Purpose

This article looks at setting up, maintaining, and learning to shoot an AR-15 carbine. The intent is to have a quick-handling, reliable rifle for shooting out to 300 yards, not a precision rifle for driving tacks from a bipod or national-match sling.

The AR-15 design dates back to the 1950s. It has some weaknesses, and several companies claim to have built a better mouse trap. They might be right. However, the AR-15 works just fine for civilian use when kept clean, lubricated, and used with good magazines. And, when you buy an allegedly better mousetrap like a Robinson Armament XCR, SIG 550 family, http://en.wikipedia.org/wiki/Adaptive_Combat_RifleRemington ACR, or FN SCAR, you’re getting a rifle with little proliferation and aftermarket support. An AR-15 gives you a very widely proliferated system with a huge ecosystem of parts and knowledge. Other options like the HK MR556 and LWRC M6 retrofit the AR-15 with a gas-piston system for cooler, cleaner operation but add a bunch of additional parts that can break, introduce new problems such as bolt-carrier tilt, and don’t address the locking lug design, tight clearances, or other perceived shortcomings of Stoner’s design. Perhaps one of these better mousetraps will eventually supplant the AR-15. Time will tell.

Approaches

The AR-15 is a very modular rifle that consists of two halves, the upper and lower, which are held together by a pair of pins. Swapping uppers and lowers takes only a few seconds. Furthermore, the actual firearm from the ATF’s perspective is the stripped lower. This is the only part that you need to purchase from a dealer. Everything else can be purchased through the mail. This results in three main approaches to putting together a rifle:

  1. Buy a complete rifle at a dealer.
  2. Buy a stripped lower at a dealer and order a pre-assembled upper and the remaining parts to finish the lower.
  3. Buy a stripped lower at a dealer and order the parts to build the upper and finish the lower.

Complete Rifles

There are several off-the-rack AR-15s that make a fine base rifle. Add a few accessories and they’re ready to go.

Rifles like the Noveske 16” Gen III Switchblock represent the top of the line with models from Bravo Company, Daniel Defense, LMT, and S&W also providing good options. S&W’s AR-15 models are readily available in gun stores and several make fine base rifles. The VTAC II and M&P15T both look like good choices. S&W doesn’t actually make the parts: they assemble carbines with parts from other manufacturers. They had some problems with their early AR that amounted to them not knowing one end of an AR from the other but hired one of the production engineers from Colt and their problems went away. To their credit, they replaced or repaired most of they early carbines.

Colt’s 6920 serves as a reference in build quality, but you’d need to spend several hundred additional dollars buying things that come standard on other models, such as a railed handguard, so it doesn’t represent a particularly good value.

AR-15s need to be kept lubricated and somewhat clean to run well, but a good one will keep running and stay manageable when hot from heavy shooting. This is where the difference between manufacturers really shows up. A cheap rifle will do fine plinking at the range, but it’s unlikely to run smoothly shooting 2k rounds over a weekend in a rifle class.

Rolling Your Own

Many knowledgeable folks buy the lower and a local firearms dealer then order a complete upper and the parts to build out the lower through the mail. This option avoids the 11% excise tax on complete firearms and provides a high degree of customization. Assembling the lower requires a set of drift punches, a small hammer, and a receiver extension nut wrench. A more ambitious option is to assemble the upper as well. This allows further customization of the rifle but also requires a vice, upper receiver block, and barrel nut wrench.

Honestly, assembling the lower and ordering a complete upper is the best option for 99% of the population.

Good sources of uppers and parts include Bravo Company, Centurion Arms, and Rainier Arms.

Barrel

Look for a barrel that’s chrome lined, a process that coats the chamber and bore with a thin layer of chrome to improve barrel life and reliability. The chrome coating is harder and more heat resistant than the underlying barrel steel. Barrel wear mostly occurs at the throat (the area right in front of the chamber) and is accelerated by heat build-up from rapid fire. Chrome is better able to resist wear in these conditions than unprotected steel. It is also more slippery, which aids extraction of spent cases as the rifle gets dirty. The one downside is that chrome plating is not as even as the underlying barrel and results in a slight loss in accuracy. But that’s only important for match shooters looking to shave off that last 1/4 MOA from their groups.

The barrels in AR-15s have twists ranging from 1:7 to 1:12. This refers to barrel spinning the bullet one complete revolution every 7 to 12 inches. Faster twists will stabilize heavier bullets at the cost of slightly increased barrel wear and possible overstabilization of light bullets. If you’re unsure of what to get, look for a 1:7 barrel. Many AR-15s ship with 1:9 barrels, and they’ll reliably stabilize bullets up to 69 gr. without overstabilizing lightweight ones, such as 40 gr. varmint bullets. This twist may not, however, stabilize heavyweight bullets like the 77 gr. one found in the Mk. 262 and many match rounds. It works fine with typical 55 gr. and 62 gr. bullets, which make up 99% of the ammunition out there. A 1:7 will stabilize 77 gr. bullets, but lightweight varmint bullets may disappear in a puff of smoke soon after exiting the muzzle.

Barrels may be chambered in .223 Remington, 5.56 NATO, or .223 Wylde. Look for one that is 5.56 NATO or .223 Wylde, as firing surplus 5.56 ammunition in a .223 barrel can result in potentially dangerous overpressure conditions. Shooting .223 ammunition in a 5.56 barrel is no problem.The Wylde chamber splits the difference and can shoot both safely.

There are four different length gas systems on AR-15s: pistol (3.5”), carbine (7.5”), mid-length (9.5”), and rifle (13”). The length refers to the distance from the chamber to the gas port; the actual tube is slightly longer. I have owned 16-inch barreled rifles with both carbine and mid-length systems, and the mid-length one has a much smoother recoil impulse and more reliable extraction cycling. This may be due to the lower peak gas pressure and slower timing of the mid-length system. I’d recommend going with a 16” barrel with a mid-length gas system.

The popular M4 barrel style seems backward to me, as it has a thin profile under the barrel and a thick one in front of the gas block. The added weight out front offers zero benefit. Bravo Company and Daniel Defense both offer lightweight barrels with Noveske offering a mid-weight option that puts more mass under the handguard.

Handguard

The original rifle design used insulated handguards that snapped in place between the upper receiver and front sight. The front sling swivel then attaches to the front sight. This means that pressure on the handguard or sling will bend the barrel, thereby chainging the point of impact. An AR-15 that I used to own shifted by a few inches at 100 yards as a result of slinging up. I’d recommend using a handguard that does not touch the barrel at all. These designs often have a square cross section with Picatinny rails on all four sides for mounting optics and accessories. I’ve had good luck with LaRue handguards and like the integral sling swivel. Installing them requires a strap wrench like this one. Daniel Defense and others make perfectly good handguards as well.

Another option is to use a one-piece upper like the Vltor VIS or Mega Monolithic. The Vltor is a work of art.

Optic

There’s not much need for magnification on the carbine we’re considering here. More important is to have an aiming system that works in all lighting conditions and lets the shooter keep both eyes open. Both Aimpoint and EOTech make optics that fit this description, and you’re not going to go wrong either way. These sights aren’t that much faster than iron sights in good lighting and when shooting from classic high-power shooting positions. But when the light fades or the position gets sketchy, red dot sights help make the shot.

Aimpoints come with either 4 or 2 MOA dots. A 4 MOA dot covers 4" at 100 yards, 8" at 200 yards, etc. The 4 MOA dot is fast but somewhat coarse from a target-shooting perspective, although you can aim with the edge of the dot at longer ranges. To put things in perspective, the 4 MOA dot covers 12” at 300 yards while the 2 MOA dot covers 6”. The dots all grow in size as the brightness increases. I have an Aimpoint ML3 with a 2 MOA dot on one of my rifles, and the dot just gets bright enough not to wash out on bright days. In increasing order of price, Aimpoint sights to consider include the CompC3, M3, T1, and M4s. The T1 + LaRaRue mount is probably the way to go for most rifles.

Most of the EOTech sights use a 1 MOA dot within a 65 MOA circle. Close up, you just use the circle. Farther away, you transition to the dot. If I went with an EOTech, I’d likely get a model that uses CR123 lithium batteries for compact size and commonality with high-intensity flashlights. Second choice would be a model with AA batteries to keep things simple. Some people prefer the EOTech over the Aimpoint due to the multi-function reticle and not having as much perception of looking through a tube. Early EOTech sights were reported to have reliability issues, but the current Revision F models are apparently good to go.

LaRue sells most of the sights mentioned above bundled with first-class mounts.

Iron Sights

Back-up iron sights (BUIS) are typically set up to be visible in the lower third of the 1x optic when deployed. The idea is that if the red dot in the optic goes out, the shooter can drop their eye a quarter inch and engage the target with the BUIS. A perennial question is whether to install fixed or folding BUIS, and in the latter case whether to keep them permanently deployed or folded down out of the way.

If fixed or permanently deployed, transitioning to them is much faster in an emergency. There’s no need to fiddle with the sights prior to using them. However, deployed BUIS makes for a busier sight picture through the optic since the sights are visible in the periphery, and they’re more likely to break off or hang up on something. This is something to practice different ways.

Troy sights are the reference for folding models, with Magpul sights serving as an inexpensive alternative. The Troy sights must be manually raised while the Magpul sights are spring loaded.

Adjustable Stock

The basic telescoping http://en.wikipedia.org/wiki/CAR-15CAR stock works well enough but trades off light weight for a rattling and poor cheek weld. The Magpul CTR uses a unique friction lock to overcome the rattling, while the ACS adds storage compartments that also provide a good cheek weld. It’s also an inch longer than the CTR, which is important for eye relief when shooting a rifle with magnifying optics prone. The Vltor IMod also provides a good cheek weld and storage compartments but rattles slightly. It’s the same length as the CTR. Vltor also makes the slightly longer EMod, which is the same length as the ACS.

Note that stocks come in two sizes: commercial and mil-spec. The size refers to the length and diameter of the buffer tube, which is the fixed metal tube that extends back from the upper receiver. The commercial tube is larger in diameter and longer than the mil-spec tube. The shorter length of the mil-spec tube can create problems when using magnifying optics due to eye relief issues. See this blog post.

Pistol Grip

I don’t care for pistol grips with finger grooves, as I find that my grip changes based on how I’m shooting and often doesn’t line with the grooves. The Magpul MOE grip works great for me.

Fore Grip

I prefer Magpul’s AFG-2http://store.magpul.com/product/MAG414/88 to the traditional vertical fore grip. The AFG-1 will bump into the rail panels on the sides of most handguards. The AFG-2 has a slimmer design to avoid this problem. The AFG-1 was the only one available when I built my carbine, and it required a good bit of filing before it would fit. There’s a good discussion of hand positions here.

Trigger

Most off-the-shelf rifles ship with a heavy single-stage trigger. A light, crisp http://geissele.com/Geissele trigger can make the rifle far easier to shoot and helps extract the maximum accuracy from the rest of the components. Their SSA and SSA-E models give up adjustability to provide a more affordable option to their DMR. I have a DMR in my 16” carbine and an SSA-E in my SBR. Both are as good as it gets.

Light

A Sure-Fire X300 Ultra is a great place to start and does double duty on a handgun. Streamlight also makes some well-regarded lights. Mounting involves making compromises. Putting the light at twelve o’clock means you can activate it with either hand and clear obstacles/barriers without the light bouncing back at you but interferes with traditional front-sight mounting. I typically put the light at six o’clock. It isn’t as handy for peeking up over barricades but retains access for both hands. A three- or nine-o’clock mount is typically only accessible with one hand and gets tricky working around corners.

Sling

Slings come in three-, two-, and single-point configurations. I can’t recommend three-point slings because they get in the way of rifle controls. Single-point slings work well for transitions between shoulders and to a secondary weapon but don’t secure the rifle well for movement. The best bet is probably a two-point model like the Vickers Sling. They’re quickly adjustable for length, manageable for transitions, and can be locked down to secure the rifle while moving. They’re also usable as a shooting sling, although nowhere near as good as a national-match sling in that capacity. Single-point slings do not function as shooting aids. The Magpul slings looks like clever designs in that they can quickly switche between single- and two-point configurations, but I haven’t tried them.

Magazines

I’ve found both mil-spec aluminum, Magpul PMAGs, and Lancer magazines to provide good reliability. The main thing to watch on aluminum magazines are the feed lips. Throw them out or clearly mark them as bad if the feed lips began to widen or crack. Nothing good can come of trying to push the lips into place. I’ve had trouble with several off-brand magazines and never tried steel ones. In general, stick with windowed PMAGs and you’ll be fine.

Magazine Pouches

Methods for carrying spare magazines including belt systems, drop-leg pouches, and chest rigs. The belt systems place the spare magazine on the belt, just as with pistol magazines. The drop-leg systems place the magazines on the outside of the thigh. This lets the shooter carry spare pistol magazines on their belt and rifle magazines on their thigh. Chest rigs place the magazines on the shooter’s chest and are often used in conjunction with belt or drop-leg system.

Lubrication

I and several friends have really taken a shine to cleaners and lubes from Slip 2000. Besides working well, they’re non-toxic, water-based, and don’t stink. I’ve used their copper cutter to clean rifle/pistol bores and their cleaner/degreaser on the receiver. I’ll give their grease and weapons lube a try once my supplies of lubes from other companies get lower. I haven’t tried their carbon killer, but it would likely make cleaning an AR-15 bolt and bolt carrier much easier. LaRue ships their uppers with Machine Gunners Lube, so I assume it is good stuff.

The bolt carrier group has to stay lubricated for smooth functioning. The AR-15’s operating cycle dumps hot gas from the barrel back into the receiver, which cooks off the oil. Hence the need to re-apply lube every 250 or so rounds. This can be done through the ejection port in a hurry, and there are two small holes for channeling lubricant down to the bolt. MILITEC-1 may be a better bet than the lubes from Slip 2000 for the bolt carrier group since it leaves behind a dry lubricant after cooking off.

Extractor

The SOPMOD extractor upgrade kit does wonders for extraction reliability. The parts in the kit increase the grip of the extractor on the case rim. The extractor can slip over the rim when the chamber gets dirty, leading to a nasty double feed. I’ve never had this happen after installing these parts in my AR-15s.

Cleaning

I’ll give my AR-15s a quick cleaning after most range trips, as they typically involve firing a few hundred rounds. The cleaning starts off by separating the upper and lower and removing and disassembling the bolt carrier group. The components get scrubbed with a brush and wiped with paper towels to remove fouling and carbon build-up before getting reassembled and lubed. I’ll push out the pin that holds the extractor in place to remove fouling from underneath it every couple of cleanings. The firing pin should be run dry. The chamber gets cleaned with a purpose-built chamber brush, which I found important when shooting underpowered, steel-cased ammunition like Wolf.

I prefer using a cleaning jag to push patches through the bore. Instead of threading each patch through the eye of a slotted tip, just push the patch onto the pointy tip and push it through the bore. There are two different thread pitches for accessories: 8x32 and 8x36. The former is used on commercial cleaning rods, the latter on military ones. Stick with the commercial threading. I’ll typically run a wet patch with copper cleaner through the barrel and let it sit while cleaning the bolt. Then I’ll alternate ten strokes with a wet brush with a dry patch until the patch comes out clean. A bore guide eases pushing wet brushes and dry patches through the barrel without making a mess of the receiver but shouldn’t be considered necessary.

It shouldn’t take more than twenty minutes to clean the rifle.

Periodically, disassemble the magazines to give them a cleaning. They should be run dry (no lubrication).

Other

Applying Blue Loctite to screws and fasteners will prevent them from loosening due to vibration. This is especially important for the screws that hold optics and back-up iron sights in place. The screws will still break free for removal or adjustment with hand tools.

Training

You’re not going to learn to run an AR-15 from a book, and your friend is probably only going to teach you bad habits. Start off by taking a course from a reputable trainer. Books and DVDs can be extremely helpful once you have the background knowledge to evaluate your progress and diagnose your problems. A good instructor is critical for reaching the point where you know what you don’t know.

Green Eyes, Black Rifles provides an excellent overview of weapon selection, shooting, and maintenance. The Art of the Tactical Carbine and The Art of the Tactical Carbine, Volume 2 provide good introductory video instruction. Magpul teamed up with the Discovery Channel, and they’re filmed as if you’re embedded in the class. The camera moves with the shooter like in a Hollywood movie and it’s filled with clear animation of important concepts. First rate! FM 23-10 is a good text on general rifle shooting. Check out Jim Owens’s books for the fine points of sight picture, natural point of aim, trigger control, doping the wind, and other rifle-shooting fundamentals. Be sure to mute your speakers before clicking on the link. His book on sight alignment and trigger control is a masterpiece. David Tubb’s The Rifle Shooter provides a graduate-level education from a match shooting perspective. It not only details rifle shooting but discusses round selection, loading, and rifle mechanics for accuracy.

My Carbine

This is a snapshot of my 16” carbine in its current configuration. This rifle has evolved considerably over the years.

Direct Impingement vs. Gas Piston

The AR-15 was originally designed with a direct-impingement (DI) gas system that vents high-pressure gas from the barrel back to the upper receiver. The gas hits the gas key on top of the bolt carrier and pushes it backward to unlock the bolt and cycle the action. Some AR-15s now sport gas-piston systems, where the high-pressure gas hits a piston that pushes back on the bolt carrier via an op-rod.

Both of these systems have their pros and cons. The biggest practical con with gas pistons is that there’s nothing close to a standard and every manufacturer has their own design. This locks you into a specific manufacturer for spare parts, and you’re out of luck if they close up shop or change their design and drop support for the old one. Perhaps the US Army will adopt a gas-piston AR-15 at some point. Then there would be a standard to rally behind as exists with the DI system. Gas pistons also seem like a solution to a problem that doesn’t exist, as DI AR-15s will run reliably if the bolt carrier group is kept lubricated.

The DI system is very lightweight and simple and effectively makes the AR-15 a gas-powered bolt-action. The gas tube is the only exception to the barrel floating free, which provides a high accuracy potential. The design is also standardized, so you can buy parts from dozens of manufacturers. The downside is that the system vents hot gas into the upper receiver, which slowly cooks off lubrication and deposits fouling. This is easily addressed by lubricating the bolt carrier every few hundred rounds.

A gas-piston system does not allow for as effective free-floating of the barrel and is also heavier, costlier, and more complex with additional parts that can break. In return, the upper receiver stays cleaner and cooler (at least when run without a suppressor) due the lack of hot gas blowback. Some gas-piston designs use a surprisingly small piston and thin op-rod compared to those on serious rifles like the Robinson XCR and AK-47.

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Last edit: 17 October 2014