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AR-15 Parts Guide

AR-15 Parts Guide

Here is a basic guide to the main component parts of an AR-15

The AR-15 is America’s Gun – The Modern Sporting Rifle

Basics about the very popular firearm the AR Platform

The AR-15 (Which stands for ArmaLite Rifle 15, NOT Assault Rifle 15) is a modern sporting rifle, and is a semi-automatic rifle that is modular in design, and made out of parts that are Steel, Aluminum and Plastic, generally. The firearm is based on the .223 Remington cartridge which is a .22 caliber bullet in a high powered rifle cartridge. The .223 Remington is very similar to the 5.56x45mm NATO cartridge. Many different AR rifles can shoot one of these cartridges, and both cartridges are considered to be the “base” or “standard” cartridge of the AR-15.

The AR Platform as it is sometimes referred to, is a light to medium duty and medium range rifle system that has been adopted by the US military as the standard issue rifle  (The M4 variant is an example of this) of the Armed Forces. It is generally characterized as having a mild recoil profile that most shooters, including many youth and small framed individuals can shoot easily. It shoots a relatively high velocity projectile and has a basic lethality range of more than 1000 meters, though, because of the lighter weight of the projectile and the small size, it is generally considered most useful out to around 650 meters/600 yards, and usually much closer than that.  It is considered to be an easy to understand, lightweight rifle that uses a modular build style that is easy to repair and maintain thanks to its straightforward design that uses a standardized parts fitment and specification.

Basic Safety information and understanding of cartridge interchangeability for the AR-15

The 5.56x45mm cartridge can also be called the 5.56NATO, 5.56×45, and is very similar to the .223 Remington. Because of specifications and very slight differences in the the way the chamber and the front of the cartridge are built, it is generally considered a best practice from a safety perspective to AVOID shooting 5.56x45mm cartridges out of a barrel that is marked as a .223 Remington. However, the barrel that is marked 5.56NATO, or equivalent is generally considered safe to fire a .223 Remington cartridge out of. Generally the .223 Remington cartridge is considered to be slightly more accurate than the 5.56x45mm, while the 5.56 is considered to be more powerful from a pressure and powder charge perspective.  Because of the SAAMI specification of the 5.56, it is considered to be unsafe to fire it in the chamber of a .223 Remington, even though, for almost all intents and purposes, the cartridges (and cartridges are sometimes called “rounds” or “ammunition” or “ammo”) are basically the same. A chamber style, called the .223 Wylde allows both cartridges to be safely fired interchangeably in the same barrel without overpressure concerns.

SAAMI Specification, the use of this guide and outside resources

SAAMI (as we briefly mentioned before), stands for Sporting Arms and Ammunition Manufacturers’ Institute), which standardizes the specifications of cartridges so they can be produced by multiple manufacturers and are safely able to be regulated from a production tolerance perspective. The link above for the SAAMI is linked to the article about the organization. This link is to SAAMI’s website. You may see other links throughout this basics guide so that you can cross reference information, and understand concepts on a broader level, with input from more than a single source. While we believe our content to be accurate and of high quality, we also believe that no one source is infallible and that all those who are researching or learning about firearms should use multiple sources. You should engage with trusted sources and double check information that is related to safety and proper firearms use, if it doesn’t seem reliable or is not issued from a trusted source.

Basic wrap up of the introduction to the AR-15

The AR-15 is one of the most popular firearms in the world and has a robust market ecosystem dedicated to modification, accessorizing and building the firearm. Because of its modular, specification based interchangeable parts, it is generally considered to be safely buildable by many shooters and enthusiasts without the help of a gunsmith or other experienced armorer.  Because of this, there are many thousands of parts for sale in the market, made by thousands of manufacturers and brands.

The AR-15 and its various brands/models and variants are generally considered to be in the style of a rifle, but the AR can be built as a pistol, or as a rifle. You will need to become familiar with your local, state and the Federal laws that govern the use of each type or style of the AR-15 in your area.

We are presenting this guide as a complete newcomer’s guide to the modular components and parts of the AR-15. If you haven’t already guessed, this is not the most interesting guide for a seasoned user or enthusiast of the AR platform per se, as it takes a novice and remedial approach to the concepts of the firearm, and is to help people who are completely unfamiliar with the AR-15 and its parts.

We educate our writers in a formal education program that sometimes starts with the basics. This guide is part of that education at the very lowest level. Don’t worry, though, we will be talking at a much more advanced level in just a few more articles or knowledge base topics.

As a plug for our organization, if you are interested in writing in the firearms industry, we have a page dedicated to that at

The basic Groupings of the AR-15 Platform parts

Basic groupings of AR-15 parts

There are four basic groupings of parts for the AR-15. These groupings are made up of other parts

They are as follows:

  • The Lower Receiver Assembly Group
  • The Upper Receiver Assembly Group
  • The Bolt and Carrier Group
  • The Magazine

When these parts are separated, you can perform all the basic field maintenance work on the firearm. Generally the AR-15 is considered an easy rifle to work on and maintain. It is held together by two pins between the Lower receiver group and the upper receiver group. The upper receiver group holds the BCG (Bolt and Carrier Group) within it and the lower receiver group holds the trigger and pistol grip and other fire control group components. 

When you view the AR-15 from its component parts groups, it’s quite an easy gun to understand. From a general perspective, the AR-15 is still an easy-to-understand firearm, as it doesn’t have that many large parts in it. As with any complex mechanical device however, there are plenty of springs, pins, and cups, and parts that work together to contribute to the overall functionality of the firearm. When you look at it from the perspective of a gun made up of a bunch of parts, it’s harder to understand, especially if you’re not looking at the parts as you’re learning about them.

Each of the above mentioned parts groups are assembled with a plethora of other parts. Below we’re going to talk about the important parts within the basic groupings.

The lower receiver assembly group generally contains the buttstock, the pistol grip, the lower receiver, the buffer tube and assembly, and the fire control group, safety selector and associated parts, like the magazine release. For the purposes of this article, we’re to stay in a basic, remedial format, and this is as far as we’ll go regarding parts density, for the time being.

The upper receiver assembly group generally contains the upper receiver, the barrel, the handguard, the barrel nut, gas tube, gas block, the sighting system and any muzzle attachments that may be on the end of the barrel. Also, when it’s not disassembled, it will contain the bolt and carrier, which is called the bolt carrier group generally. It also includes a charging handle and components surrounding the ejection port and the forward assist. Some parts are not available on all variants of the AR-15. For instance some specialty builds of the AR-15 do not have a forward assist or an ejection port cover, while many mainstream variants do. 

The BCG or bolt carrier group contains the bolt which contains the extractor and ejector and holds the firing pin, and the carrier which has a gas port key which fits into the firing mechanism which utilizes, on many guns, a part called a direct impingement gas tube. This is a part contained within the forend or the handguard above the barrel, generally. In many variants of the AR-15 the firearm operates on a direct impingement or DI gas redirection principle. 

In some other variants of the AR-15, the firearm operates on a Pure Gas system which involves a gas block and a plunger which actuates the firearm to allow it to continuously fire in a semi-automatic format. For our purposes we’ll be talking about the direct impingement model for the most part. Some articles on this website will reference a gas build or a piston system which utilizes a piston or plunger as previously mentioned to actuate the reverse motion of the bolt and carrier. Each system has their advantages and disadvantages, for the most part. Both systems have been proven to be quite reliable in their own right, and for the most part, a direct impingement system is generally cheaper and almost as reliable as a gas piston system. We’re trying to maintain the accuracy of the statements in these basic Firearms guides; therefore we’ll refrain from giving opinions about what we believe to be better parts or builds. Generally, this is a guide to help you understand the component parts of a basic AR-15 rifle.

The magazine is the fourth component group which is evident when you make a field stripping of the AR-15 rifle. The magazine is made up of a magazine body, a magazine floor plate, a magazine spring, and the magazine follower. The cartridges that shoot out of the AR-15 rifle are stored within the magazine, and the magazine provides upward spring pressure to ensure that a semi automatic firing capability is maintained. That is to say, that for every one pull of the trigger a single cartridge is fired, and then a new cartridge is fed into the chamber, and the old cartridge has been ejected.

The term field stripping we used above, refers to the idea of being in the field or being out somewhere and being able to take apart the firearm. Historically the easiest way to do this quickly, was to take the tip of a cartridge and push the pin from one side out into the other side allowing the 2 receiver groups to disassociate or disassemble from each other. Pulling the bolt carrier group and the charging handle out of the back of the upper receiver group would constitute, along with removing the magazine from the lower receiver group, a field stripping. Having the rifle field stripped makes it much easier to maintain, address wear and tear concerns or monitor for wear and tear, and to clean the rifle.

There are plenty of other parts that go into the final build of the AR-15 but for the purposes of this article, these are the main component parts.