AR 15 Parts Explained: The Beginners Walk Thru

The AR-15: America’s Rifle

The AR-15 is widely considered America's Rifle. The AR platform is an easy-to-assemble and use shooting system. It is an excellent tool for sports and defense alike. Versions or variations of the rifle are still being used by law enforcement and special operations units all across America.

The AR platform is a great place to start, no matter the style of rifle you want. You can quickly build, assemble, tear down, clean, and work on your AR Rifle with simple tools. The AR-15 will be the weapon of choice for many Americans for years. If you do not have one, get one.

Quick Breakdown of the Most Common AR 15 Configuration

The first thing to look at when discovering the AR-15 is the standard. The standard or most common configuration of an AR15 containing the essential parts is a Carbine length AR15 rifle with a standard 16" barrel. It typically also has a collapsible stock. The most basic  AR-15 parts are Mil-Spec. This includes the receivers and accessories. The handguard and optics will vary wildly, even for the most common and basic AR15 rifles.

The most basic components are mil-spec. Custom accessories like grips, flash hiders, floating handguards, rails, fore grips, slings, and flashlight mounts come in aftermarket grade but are often no less impressive. It would be best to always start with the standard, no matter how you want to build your weapon. The middle is the most reliable and best version for almost all circumstances. It never hurts to have a standard rifle.

What Does the “AR” Stand for in AR 15?

The AR in AR 15 stands for Armalite Rifle. It does not stand for, as some would have you believe, Assault Rifles. The AR-15 Rifle is not an assault weapon. It fires a single bullet with each of the trigger pulls. It was meant and is classified as a home defense weapon.

The Armalite rifle platform was designed as a semi-automatic version of the M16. It was always intended for civilian use, while the automatic version was meant for military use. The AR15 rifle was made for sporting, law enforcement, and personal and home defense.

Colt purchased the Armalite Rifle patent. But please don't worry; you do not need to shop all over the internet for Colt Ar-15 design products. The lightweight selective-fire rifle has become an open-source platform, and many firearm manufacturers are using the design to create many variations. Mil-Spec is considered original equipment, so you do not need to fuss over looking for any particular manufacturer.

The AR platform is an excellent rifle for anyone who wants to understand, clean, and use a gun for a specific purpose. Due to the multitude of customization and modifications, the AR is the rifle of choice for today's shooters.

What Sort of Ammo Does an AR 15 Use?

The most common AR-15 will typically use .223 or 5.56 ammunition. These rounds are Mil-Spec and, therefore, the most common. 

Please check your rifle before loading. Using the wrong ammunition can be costly. Here is a much more complete list (from Wikipedia) of the different ammunition rounds that can be used with an AR-15.

Rimfire Cartridges

• .17 HMR
• .17 Mach 2
• .17 Winchester Super Magnum
• .22 Long Rifle
• .22 Winchester Magnum Rimfire

Centerfire Cartridges with Imperial Measurement

• .17 Mach IV
• .17 Remington Fireball
• .17 Remington
• .17-223
• .20 Practical
• .20 GPC (wildcat)
• .22 GPC (wildcat)
• 22 Grendel (wildcat) aka 224 Grendel
• .22 Nosler
• .22 PPC
• .204 Ruger
• .222 Remington
• .223 Remington
• .223 Winchester Super Short Magnum
• .224 Kritzeck
• .224 Valkyrie
• .24 GPC
• .243 LBC
• .243 Winchester Super Short Magnum
• .25 Winchester Super Short Magnum
• .25-45 Sharps
• .257 Ocelot (wildcat)
• .25 GPC (wildcat)
• .26 GPC (wildcat)
• .27 GPC (wildcat)
• .277 Wolverine (semi-wildcat)
• .277 MSR (Dasher Wildcat)
• .28 GPC (wildcat)
• .30 American
• .30 Carbine
• .30 GPC (wildcat)
• .30 Remington AR
• .30 Sabertooth (wildcat)
• .300 OSSM
• .300 AAC Blackout (7.62×35mm)
• .300 Whisper
• .300 HAM'R – Wilson Combat
• .338 SOCOM (wildcat)
• .338 Spectre (wildcat)
• .350 Legend
• .357 Automag (wildcat)
• .358 SOCOM (wildcat)
• .358 Yeti (wildcat)
• .375 Stalker (wildcat)
• .375 SOCOM
• .400 AR (wildcat)
• .40 S&W
• .44 Automag (wildcat)
• .44 Remington Magnum (wildcat)
• .44 SOCOM (wildcat)
• .440 Corbon Magnum (wildcat)
• .45 ACP
• .450 Bushmaster
• .458 SOCOM
• .475 SOCOM (wildcat)
• .499 LWRC
• .50 Action Express
• .50 Beowulf
• .50 SOCOM (wildcat)

Centerfire Cartridges with Metric Measurement

• 5.45×39mm
• 5.56×45mm NATO
• FN 5.7×28mm – PDW
• 6mm Mongoose (wildcat)
• 6mm ARC – rifle
• 6mm Dasher
• 6mm AR (wildcat)
• 6×45mm – intermediate
• 6.5mm Grendel
• 6.5 Timberwolf (wildcat)
• 6.8×39mm (.277 Wolverine)
• 6.8mm Remington SPC
• 7mm Valkyrie (wildcat)
• 7.62×33mm (.30 Carbine)
• 7.62×37mm Musang (wildcat)
• 7.62×39mm
• 7.62×40mm Wilson Tactical
• 7.92×33mm Kurz
• 9×19mm Parabellum
• 9×39mm
• 10mm Auto (10×25mm)
• 10mm SOCOM (wildcat)

How Does an AR 15 Operate?

The standard AR-15 is a gas-operated rifle. It uses a small amount of the gas from a fired round to actuate, removing the spent round and replacing it with a live band. It does this with a gas impingement system that captures some gas from the fired round through a hole in the barrel. The gas is then redirected using a gas block fastened to the barrel and sent through a gas tube back toward the shooter.

The gas sends the bolt carrier group (BCG) backward. The  BCG removes the spent cartridge and discards it through the opening in the upper receiver. The BCG is immediately sent back forward using the spring in the buffer tube inside the stock. The BCG then loads a live round into the barrel provided by the magazine.

Gazing at the Gas System

The gas system is one of the parts of the AR-15 rifle that makes it so desirable. It is what enables the gun to be semi-automatic. The gas system is often made from a gas block and tube.

Gas tubes come in different lengths, such as:

• Rifle-length
• Mid-length
• Carbine-length
• Pistol-length

Gas Blocks Come in a few Different Ways as well, such as:

AR 15 

• low-profile
• adjustable
• front sight post

Gas Impingement vs. Gas Piston Operation.

Both systems work on similar principles. Gas actuates the rifle's action. With the impingement system, gas travels and actuates the BCG. This allows more residue to accumulate on the BCG and other parts inside the Upper receiver.

With a gas piston system, the gas actuates a piston that travels and actuates the BCG. This system is cleaner as it does not allow residue to form or accumulate in the upper receiver.

How Do All the Parts Work Together to Operate an AR 15?

All the parts on an AR 15 work together to fire one round with each trigger pull. Here is a quick and dirty walk-through of how the pieces function together.

How AR 15 Parts Function Together:

• Live rounds are loaded in a spring-loaded magazine
• The magazine is loaded into the lower receiver of the AR 15
• The live round must be physically loaded in the barrel
• By pulling the charging handle back and releasing it
• The charging handle pulls back the BCG
• When released, the spring in the buffer tube pushes the buffer and BCG forward
• The BCG will move the top round from the magazine and chamber it into the barrel
• The trigger can then be squeezed, and the round fired
• from there, some of the gas from the spent round will be captured
• by a hole in the barrel and redirected into the gas tube by the gas block
• The gas in the tube will push the BCG back, removing the spent round
• then immediately be pushed back forward by the spring in the buffer tube
• loading the next round from the magazine, and so it goes.

What is the Difference Between a Fully Automatic and Semiautomatic Rifle?

The difference between fully automatic and semiautomatic rifles is a felony charge, significant fines, and time in prison. All joking aside, the two have a severe and essential difference.

Semi-automatic rifles will fire exactly one round per trigger pull. But many rounds can be fired, one after another, if the trigger is pulled rapidly.

Fully automatic rifles will continue to fire as many rounds as are available in the magazine or from a belt as long as the trigger is pulled.

What Does the Forward Assist Do on an AR 15?

A forward assist on an AR 15 is a way to get yourself injured or killed. Why do we say that? Because it is a design carryover from the military version. The idea behind the assist was that if the rifle was so dirty that the BCG got stuck loading the next round, it might need to be jammed or forced into place.

This seriously only applies if you have a filthy weapon in combat situations, an enemy is closing in, and it is a life-or-death situation. Otherwise, stop and clean your rifle if the BCG or any other part of the rifle is too dirty to operate correctly.

Exploring the Operating Handle

The operating handle, or charging handle, charges the rifle. It is one of the most essential parts and pulls the BCG backward. This can be done to remove or load rounds into the barrel.

They do not move when the rifle is operating under normal conditions. The charging handle can have standard actuation, ambidextrous capabilities, or extended handles for easier use with gloved hands.

Charging or operating handles come in many colors, models, and designs. By shopping for AR 15 charging handles, you can find more of what you want.

A look at Iron Sights

Backup iron sights are the mainstay of rifle must-haves. They are standard and essential parts. It does not matter if you like to use the most sophisticated optics available; backup iron sights are invaluable if your batteries fail. The primary function of the rifle is to deliver a bullet accurately and very fast. Having iron sights is a great and inexpensive insurance policy.

There are so many different types to choose from that there is no reason not to have a pair. They come in a 45-degree offset if you want them out of the way most often. They come in polymer if you want something other than the extra weight of steel. They even come as flip-up sights if you want them out of your line of sight while using your favorite optic.

Don't Overlook the Buttstock

An essential but often overlooked component for AR-15 builds, the buttstock is a critical piece. You may regret picking one that is too heavy, short, light, narrow, snaggy, cheap, or dated. It is a big part of the rifle; you will think less of your weapon if you hate your buttstock. Sure, it does not change the operation much, but it will affect the operator's mind.

Watch Your Lower Receiver

The lower receiver is the only part that contains a serial number. That means that of all the parts of your weapon, the lower receiver is the part that is considered a gun. It is the part that you cannot loan to friends, have stolen, or lose. It is the part that is registered to you. It is what takes the background check to purchase and is the most regulated.

Keep your lower receiver safe. It is the most valuable and most challenging to replace. You can easily purchase any other parts required to build an AR15 over the internet and have them shipped directly. The one part that you must buy from an FFL is the lower receiver.

You can order a lower receiver online, but you'll need to get it from a local FFL dealer near you. All other components can be traded or purchased however you like.