The AR-15 gets a lot of attention, good and bad, but there’s no denying it’s currently the most popular firearm platform in the country. Not only is the AR-15 incredibly versatile but it’s available in practically endless calibers. It’s highly customizable, right down to its trigger pins, and thanks to a variety of barrel lengths it can be used for everything from CQB to hunting to long-range shooting. The odds are good you have an AR-15 in your collection. But whether you do or not, how much of the AR-15 terminology do you know? We’re here to lend a gun-friendly hand with this AR-15 terminology list.
A2 Style Front Sight
This is a term you’ll hear occasionally, mostly from the AR owners who like retro builds. The A2 Style Front Sight was the original front iron sight on the AR platform and has a slanted A shape when viewed from the side. This is the sight used in conjunction with a carry handle. It’s become less common for guns to ship from the factory with this style of sight unless it’s specifically a retro build, but it’s not unheard of.
AR-15
There’s really no better place to really get into it than with the name of the platform itself. Despite some claims to the contrary, the “AR” in AR-15 doesn’t stand for “assault rifle,” it stands for Armalite Rifle. This is because Armalite is the name of the company that developed the platform back in the 1950s.
Barrel Nut
The barrel nut is a circular component that fits over the barrel and screws onto the front end of the upper receiver. It’s there for the purpose of helping secure a free-floating barrel. Many different styles exist, so before you try to work on your AR-15, find out exactly which armorer’s wrench is needed.
Bolt
The bolt is an integral part of the AR-15 that holds the firing pin, extractor, and possibly the ejector. It’s a tubular metal part that’s encased by the bolt carrier and located in the rearward portion of the upper receiver.
Bolt Carrier
This is the part of the rifle that holds the bolt, which you need to fire the gun. The bolt carrier is a hollow tubular piece of metal that’s located in the rearward part of the upper receiver.
Bolt Carrier Group
The term “bolt carrier group” is often shortened to its acronym, BCG. This is a term that refers to the entirety of the parts: the bolt and all its tiny pieces and the bolt carrier that holds it.
Buffer
The buffer is a tubular component that contains weights, the weight and length of which varies based on the specific caliber and design of the AR-15 in question. It fits in the forward end of the buffer spring and serves the purpose of mitigating felt recoil and using its bulk to help the bolt cycle properly.
Buffer Spring
This is the part mentioned above in the description of the buffer. The buffer spring sits in the buffer tube and holds the buffer at the forward end. The type of wire and its length depends on the specific gun. This spring is designed to work in conjunction with the other parts to mitigate felt recoil and help cycle the bolt.
Buffer Tube
The buffer tube is a hollow cylindrical tube that screws into the rearward part of the lower receiver. It contains the buffer spring which contains the buffer itself. On an AR-15 rifle or carbine, a stock is attached over the back end of the buffer tube (in some designs the buttstock is integrated into the buffer tube itself).
Carbine
In the AR-15 world, a carbine has a barrel length under 18 inches, typically 16 inches (you do find guns with 18-inch barrels marketed as carbines). These are extremely common and are popular for truck guns, home defense, and really any shooter that wants an AR-15 that’s easier to maneuver.
Charging Handle
As you might have guessed from its name, the charging handle is the part of the rifle used to chamber a round. It’s a T-shaped component located at the uppermost back end of the upper receiver. To operate it, the user grips it with their finger or fingers and pulls it sharply rearward, releasing it to allow it to fly forward under its own power. Charging handles might have one or two levers (for ambidextrous access) and come in a wide variety of styles.
Dust Cover
The dust cover on an AR-15 is a rectangular piece of metal with hinges at its base that’s used to protect the gun’s chamber from dust and debris. Not all AR-15s have a dust cover, some are simply left open. Even AR-15s that do have a dust cover are used with the dust cover open all the time. It’s a matter of personal preference combined with the risk of obstructions and dirt where the user is located.
Gas Block
The gas block is a small part with a hollow middle that slides over the barrel and fastens over a tiny hole in the top of the barrel called the gas port. The block helps regulate the flow of escaping gases to cycle the bolt.
Gas Tube
The gas tube inserts into the back of the gas block and is placed over the top portion of the barrel. It’s a long, hollow tube that the escaping gases travel through to cycle the bolt. Gas blocks are open at the back end where they insert into the receiver and closed at the front end where they fit into the gas block, with the exception of a small hole at the front end that allows the gas to travel.
Handguard (Free Floating)
On an AR-15, the handguard is a hollow tube of varying length that attaches to the front end of the upper receiver. A free-floating handguard attaches to the receiver and encases the barrel and gas tube but doesn’t come in contact with either of those parts. That means it doesn’t interfere with barrel harmonics. The handguard not only protects the barrel and gas tube but also helps protect the user’s hands from heat.
KeyMod
KeyMod was designed in 2012 by VLTOR and Noveske. It’s a cutout shape found in handguards that is used to attach compatible accessories to handguards. KeyMod is recognizable because it has a shape similar to that of old-fashioned keyholes. Unlike M-LOK, KeyMod is open source, meaning manufacturers don’t have to get licensing to utilize it on their products.
Lower Receiver
The lower receiver is located beneath the upper receiver and contains the trigger and safety mechanism/selector switch. The pistol grip extends from the underside of the lower receiver and the buffer tube and stock are attached at the back of it.
M-LOK
An M-LOK compatible handguard is one that’s been cut to fit the M-LOK system. This system is recognizable thanks to its elongated cutout shape with rounded edges, a bit like a capsule. M-LOK is evenly shaped (one end isn’t wider than the other). It was designed in 2014 by Magpul and has become the most common accessory system used on the AR-15.
Picatinny Rail
This is the rail found on most AR-15s. It’s compromised of evenly spaced, squared-off bars that are used to mount accessories such as optics to the gun. The Picatinny rail is also called MIL-STD-1913. Sometimes the Picatinny is placed only over the receiver, sometimes it extends down the entire length of the handguard, and sometimes it’s found only in small sections at either end.
Upper Receiver
The upper receiver is the uppermost portion of the AR-15’s receiver set. It holds the BCG and mounts on top of the lower receiver. The barrel is attached at the front end of the upper receiver.
As you might have guessed, this is not an exhaustive list. It’s only meant as a starting point to give you an idea of the basics of the AR-15 platform.
