The American company ArmaLite invented both the AR-10 and the even more popular AR-15. Both these semi-automatic rifles get their AR prefix from ArmaLite Rifle.
The AR-10 is now over 60 years old and was originally developed in the 1950s as a 7.62x51mm basic infantry rifle. It included features from older designs, a lightweight chassis, and a new gas system.
ArmaLite designed the AR-15 in the late 1950s as a lightweight AR-10 type gun around 5.56×45mm NATO ammo. ArmaLite had financial problems and sold the rights to Colt, who made some changes and started mass producing it and selling it.
The AR-15 is a semi-automatic rifle. Pull the trigger once; it fires once and no more than that. Companies other than Colt started making after-market accessories such as different pistol grips, handguards, scopes, buttstocks and more that could integrate with the AR. And many of those companies found they could make entire AR-15s.
An AR-15 is like a car that you can upgrade/customize by putting in seats, engines, wheels and more from virtually any provider. The reality is that unless you’re a specialist like a car mechanic, you probably won’t be able to customize your car more than tinting your windows or putting in different color floor mats. A mechanic might put custom wheels, etc. Chances are you won’t be able to mount your own car seats. But what if you could? Not only that, what if the seats you could put in one car would fit in any car? AR-15s are a bit like that. AR-15s are extraordinarily modular high-capacity gas-operated semi-automatic guns. You can take various components that fit one AR-15 and fit them to just about any other AR-15.
Due to this ingenious customizability, ARs are rightfully declared as an engineering marvel. You can buy one that’s fully built, of course, or you can assemble one yourself from the components you choose. Customization is easily done by a gun owner without requiring going to and paying for a gunsmith to do the work. Depending on what you are doing, you might need no tools or, worst case, some very simple ones.
AR-15s are so popular with the public and with gunmakers that it might probably harder to find an arms manufacturer that doesn’t make one than one that does. Ironically, however, Colt has gotten out of the AR-15 game as there is a seeming glut of these guns now. But Colt still retains the right to the name.
The heart of an AR-15 is its receiver. The receiver is the gun’s core and most everything attaches to it. To facilitate maintenance, upgrades, etc., the AR’s receiver is actually split into two parts, called, logically enough, the Upper Receiver and Lower Receiver. The two parts are joined by two pins. Better quality ones tend to have less wobble than lower quality ones.
Both upper and lower receiver are typically forged from 7075-T6 aluminum. 7075-T6 is an aluminum zinc alloy developed by Japan for the Imperial Japanese Navy’s World War II aircraft. The upper and lower receiver are normally matte black. But many companies provide theirs in all kind of colors. Field Dark Earth (FDE) is probably most common. But you’ll see all kinds of colors including white, pink, blue, etc. Many of the guns have camouflage finishes and some have rather decorative finishes like American flag motifs that often extend across the handguard and other parts too.
The receiver has several standard connections that permit attaching compatible sights, barrels, handguards, pistol grips and stocks. So you can buy the gun one way and then change any combination of parts as your budget and desires carry you.
While the standard AR-15 is used with 5.56×45mm NATO ammo, many AR type guns are offered in .22 LR all the way up to much more powerful hunting calibers. With the AR, you can swap out the upper receiver and barrel to work with different calibers in no time.
You have many choices of barrel lengths. Typical length is 16”, but you can get both longer and shorter. Longer barrels make the gun heavier and more difficult to wield, but offer more acceleration, higher exit velocities and increased accuracy.
Some barrels are threaded. These come with either a threaded cap and/or a muzzle brake or flash hider that mitigate recoil forces, muzzle flip and flash visibility respectively. The A2-type birdcage muzzle brake is a very common one. Muzzle brakes typically have one, two or three chambers.
As with muzzle brakes in artillery or tank guns, the chambers vent propellant exhaust gases to the sides and often up via vent ports as well. Upward venting provides downward thrust that helps relay the gun for faster cycling. Guns usually don’t have porting on the bottom since that might kick up dust when used in a prone position.
Most ARs have a ported M-LOK matte black handguard. The ARs usually sport a long integral Picatinny (MIL-STD-1913) rail for mounting scopes, etc. that crests the receiver and sometimes part of the handguard too.
AR-15s are semi-automatic rifles. As mentioned before, pull an AR-15’s trigger once; it fires once. But how? Simple. The system uses exhaust gases to move several parts to put the next round in place. There are two ways to do this: direct impingement or piston. Let’s briefly cover each.
With direct impingement, an AR-15’s gas system takes some of the gas that propels the bullet through the barrel and vents it through a hole (gas port) in the top (near the middle) of the barrel. The exhaust goes up the hole, into the gas block and then into the gas tube that blows back into the upper receiver. The bolt carrier group normally blocks the ammunition that’s in the magazine below. But the gas rams back (impinges) the bolt carrier group far enough to allow the next round of ammunition to spring up from the magazine into the chamber.
The first AR-15s were direct impingement. Even now most still are. However, now some AR-15s use more expensive and heavier, but cleaner operating, pistons. To oversimplify a bit, the piston essentially takes the place of the gas tube in the direct impingement system. Pistons also benefit by being more weatherproof. But their function is the same: to use exhaust gases to chamber the next round.
AR-15 pistol grips are usually black textured polymer. But they can also vary. For instance, the Magpul MOE grip has a beavertail backstrap for improved comfort and handling. It’s also hollow permitting storage through its bottom cap.
These are just some of the different aspects of AR-15s. But there is plenty more such as varieties of sights, barrel lining, types of alloys, types of handguards, types of finish, stocks, grips and more we plan to cover in other articles.