Purpose
This article looks at setting up, maintaining, and learning to shoot an AR-15 carbine. The intent is to have a fast-handling, reliable rifle for shooting out to 300 yards, not a precision rifle for driving tacks.
The AR-15 design is essentially unchanged since the '50s. It has some weaknesses, and several companies claim to have built a better mouse trap. They might be right. However, the AR-15 works well when kept clean, lubricated, and used with good magazines. And, when you buy a better mousetrap like a Robinson XCR, Sig 556, Remington ACR, or FN SCAR, you're getting a rifle with little proliferation and aftermarket support. When you buy an AR-15, you are getting a very widely proliferated system with a huge ecosystem of parts and knowledge. Other options like the HK MR556 and LWRC M6A2 are essentially AR-15s retrofit with a gas-piston system for cooler, cleaner operation. Perhaps one of these better mousetraps will eventually supplant the AR-15. Time will tell.
Rifle Basics
There are several things to look for in a carbine.
Chrome-lined 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.
Barrel twist: 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. Most AR-15s ship with 1:9 barrels that will 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.
Iron sights: Optical sighs have become extremely reliable, but a set of back-up iron sights are still important should the optic go down. The rear sight should fold down. There are different schools of thought with the front sight. Some people like a fixed front sight and set up their optic so that the dot nearly lines up with the post. This permits using the optic as a giant ghost ring if the electronics give out. Others prefer a front sight that folds down and out of the way. A disadvantage of a fixed front sight is that it limits the length of most handguard designs. It’s common to see folding front sights attached to the front of 9" or longer handguards.
Free-float 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. I've seen it change a few inches at 100 yards by 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.
Stock: Go for a collapsable stock over a fixed A1 or A2 style one. The basic telescoping CAR 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 Modstock also provides a good cheek weld and storage compartments but rattles like the CAR stock. 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.
Off-the-Shelf Rifles
There are several off-the-rack AR-15s that would make a fine base rifle. Add a sling, optic, mount, and a few accessories and it’s ready to go. There’s a good comparison of several models here.
Rifles like the Noveske N4 light recce low-profile are about as good as it gets. Note that it’s a $2k rifle. Sabre Defense makes first-class rifles but are hard to find due to DoD orders. LMT also produces excellent rifles for the DoD, but their rifles are more readily available to civilians. Colt's 6920 is a reference in build quality, but you need to spend an additional few hundred buying things that come standard on other models, such as a rail system and flip-up rear sight.
S&W's AR-15 models are readily available and otherwise a good start. A version like the M&P15T with folding front and rear sights and a quad-rail handguard would be a good choice. S&W doesn't actually make the parts: they assemble carbines with parts from Stag, DPMS, et al. They had quite a few problems with their early ARs, which amounted to them not knowing one end of an AR from the other. Then they 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. The main potential downside of S&W’s models is that they use a 1:9 twist barrel.
AR-15s need to be kept clean, 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.
Many knowledgeable folks buy a lower and a local gun shop and order a complete upper and the parts to build out the lower through the mail. You also avoid the 11% excise tax on complete firearms by going this route. But you need to know what you're doing with this option.
Optics
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 better than iron sights in good lighting and when shooting from classic high-power shooting positions. But when the light fades or positions involve shooting from the weak side (i.e., the left side if right handed), rollover prone, or around barricades, then the red dots greatly ease making 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. It’s fast but somewhat coarse, although you can aim with the edge of the dot at longer ranges. I have an Aimpoint M3 with a 2 MOA dot on one of my 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 get a model that uses AA batteries to keep things simple. Second choice would be a model with 123A Lithiums, which are the standard for high-intensity flashlights. Many people prefer the EOTech as there’s not as much perception of looking through a tube.
LaRue sells both of these sights 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 keep the BUIS permanently deployed or folded down out of the way.
If 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 both ways.
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.
The DI system is a very lightweight and simple one that 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. Many designs use a surprisingly small piston and thin op-rod compared to those on military rifles firing intermediate-power rounds like the Robinson XCR and AK-47. This doesn’t inspire confidence.
Gas System Length
There are three types of gas systems on AR-15s: carbine (7"), mid-length (9"), and rifle (12"). The distance refers to the length of the gas tube. 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 cycling. This may be due to the lower peak gas pressure and slower timing of the mid-length system.
Lights
I don’t know enough about weapon-mounted lights to make strong recommendation, but Sure-Fire makes fantastic hand-held lights and is likely a good place to look for weapon-mounted ones. As a rule of thumb, figure on about two lumens per meter when deciding the power of the light.
Slings
Slings come in 3-, 2-, and single-point configurations. 3-point slings are pretty slick but often 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 2-point sling like the Vickers Combat Sling. It’s quickly adjustable for length, manageable for transitions, and can be locked down to secure the rifle while moving. It is also usable as a shooting sling, although nowhere near as good as a national-match sling in that capacity. Single-point slings are purely for carrying the rifle; they’re not a shooting aid.
Magazines
I’ve found both mil-spec aluminum and Magpul synthetic magazines to provide excellent 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.
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.
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 is probably a better bet than the lubes from Slip 2000 for bolt carrier group lubrication since it leaves behind a dry lubricant after cooking off.
Cleaning
Unlike most of my pistols, I’ll give my AR-15s a quick cleaning after every range trip, which typically involve firing a few hundred rounds. The cleaning starts off with separating the upper and lower and removing and disassembling the bolt carrier group. The components of the bolt get scrubbed with a brush to remove carbon build-up before getting reassembled and lubed. Also push out the pin that holds the extractor in place to remove fouling from underneath it. The firing pin should be run dry.
It’s extremely important to clean the chamber using a purpose-built chamber brush. I had all sorts of extraction problems prior to doing this.
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, add cleaning fluid, and push it through the bore. Much easier! 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. A bore guide eases pushing wet patches through the barrel without making a mess of the receiver.
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 and 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 are as good as it gets in training DVDs. 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 a rifle, and The Art of the Rifle also makes a good intro text but leaves out a lot of important things. 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.
My Carbine
This is a snapshot of my carbine in its current configuration.
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Last edit: 24 March 2009