AR15 Nomenclature & Common Terms

Breakdown of the most common AR15 buzz words.

Whether you’re an experienced owner or brand new to this world, AR15 nomenclature & common terms are important to know. They help you fully understand the AR15, leading to a safer and more enjoyable experience.

AR15s can be used for personal defense, hunting, or even just a fun gun to take to the range.

ar15 terms nomenclature

If you’re someone who is looking to learn more about the AR15 nomenclature and common terms about it, this article is definitely one you should keep reading. Let’s dive in!


First, let’s talk about what an AR15 actually is. The “AR” part of the name actually stands for ArmaLite Rifle

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There is nothing about this type of firearm that makes it an automatic rifle or assault rifle, which are two common misconceptions about what the “AR” stands for.

Upper Receiver

At a high level, the AR15 can be broken down into three main systems (Checkout our diagram of the AR15). The first is the upper receiver.

ar15 upper assembly

This part of the AR15 houses multiple parts, including the following: 

  • Bolt Carrier Group 
  • Gas Block and Tube 
  • Charging Handle
  • Dust Cover

Lower Receiver

The second main system of an AR15 is the lower receiver. This is probably the most important piece of the entire AR15, as it’s what’s actually considered a firearm.

ar15 lower assembly

It’s made up of these parts: 

  • Trigger Assembly
  • Safety
  • Takedown Pins
  • Buffer
  • Buffer Tube

Barrel Assembly

The third main system on an AR15 is the barrel assembly. This common AR15 term refers to the part of the gun that is made up of the following components: 

  • Barrel 
  • Hand Guard
  • Front Sight

All of this connects to the upper receiver. 

One thing to note: To count as an AR15 barrel, it has to be at least 16 inches long.

Direct Impingement System

All AR15s are operated using a gas system of some sort. There are two main kinds, with the first being a direct impingement system.

ar15 gas system

This system takes gas released at the front of the barrel and routes it directly to the bolt carrier group in the upper receiver.

How It Works:

  • The bolt is moved
  • The spent casing is ejected
  • A new round is loaded into the chamber
  • The gun is ready to fire its next round

Gas Piston System

The second option is a gas piston system. It has the same concept as the direct impingement system, as it captures and routes gas from the barrel when you fire the AR15.

However, instead of routing the gas all the way to the bolt carrier group, it instead routes it to a piston. The piston then moves the bolt carrier group and cycles the weapon.

The main benefit to this is that it keeps your gun a bit cleaner since no gas or residue makes it to the bolt carrier group.

Semi-Automatic AR15

Semi-automatic refers to how frequently the gun will fire a round with one trigger pull. All AR15s are semi-automatic weapons, meaning that when you pull the trigger, only one bullet will fire.

This then automatically cycles the weapon and gets it ready to fire the next single round with a pull of the trigger.

Semi-Automatic Vs. Fully-Automatic

This is different than fully-automatic rifles, where you only need to pull the trigger once in order to shoot the entire magazine worth of ammunition.

Semi-Automatic Vs. Other Types

It’s also different than other firearm types, where you have to cycle the weapon manually before it can be fired again (think bolt action rifle or pump shotgun).

Field Stripping the AR15

Another common AR15 term people talk about is field stripping. This means that they are taking their AR15 apart as much as they can without the help of extra tools.

field stripping ar15

The main reason you’d want to do this is so you can clean your weapon. It’s important to clean your AR15 often, with the best frequency being after every shooting session.

Another common reason to do this is to check your firearm for any damages. If you’re shooting it and it isn’t functioning properly, it’s important to unload the weapon, make sure it’s safe, and then field strip it to check for broken components.

Picatinny Rails

One piece of AR15 nomenclature thrown around a lot is Picatinny Rails. These rails are one of the most common rail systems found on an AR15 and are designed and constructed to work with a ton of different accessories.

Different sights, grips, flashlights, lasers, and more are all great to put on a Picatinny rail system.

ar15 pictinny rail system

One cool part of the AR15 world is that you can now 3D print a ton of different accessories and attach them to your Picatinny rail system. For a full list of examples (like your new favorite beer holder), check out this article: (

Magazine and Ammunition

The magazine is the part of the AR15 that holds all your ammunition. Typically, you’ll see magazines that can hold 30 rounds of ammo. However, there are all different sizes, ranging in capacities anywhere from 10 rounds all the way up to 100 rounds.

As for ammunition, there are a few different calibers that different AR15s will be able to fire. The two most common are .223 Remington or 5.56 x 45mm. Both are solid options and will come down to personal preference to decide between.

Charging A Round In The Chamber

One AR15 nomenclature and common term you’ll hear a lot is charging a round in the chamber. This term refers to the action you do to load a round into the chamber where it will be fired from.

charging ar15

This is how you do it: 

  • Pull back the charging handle 
  • Let it slide forward to load a round into the chamber. 
  • Release the safety, 
  • Pull the trigger when ready

With an AR15, the only time you’ll have to do this is at the start of a new magazine. From there, the gun will cycle itself without having to charge a new round manually.

Sometimes, in the case of a jam, you may need to use the charging handle in order to eject a round, but make sure to do so carefully and while pointing the firearm in a safe direction.

Conclusion On AR15 Nomenclature & Common Terms

We know that the world of AR15s can be confusing at first. However, AR15 nomenclature & common terms go a long way in helping it be less confusing. 

With any luck, the previous 11 terms and their definitions should give you the knowledge you need to talk about AR15s and also use and maintain them safely.

Make sure to check out the other article we talked about earlier to get some more awesome info on the AR15 platform and its accessories!

Written By

Dan M.
Latest posts by Dan M. (see all)
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