Introduction to the AR-15

An AR Pistol. 11.5 inch barrel and an arm brace.

If you wanted the history of the AR-15, I’m not covering that here. I am writing this to give new gun owners or people new to the AR-15 platform a general overview.

Lets start by breaking the AR-15 down into two main 2 components. The upper and the lower receivers as groups. The Upper receiver is as described. It is on top. Same for the lower receiver, it is the lower half. (Pictured below)

The lower is where the serial number is located and the lower receiver needs to be assembled as a pistol or a rifle lower. The lower can be purchased through an FFL (Federal Firearms License) dealer. Which most gun stores are. (Yes, a lower can be purchased online, but needs to be shipped to an FFL in order to complete the transaction.) The lower receiver itself is the only part of the firearm that needs to be purchased through a licensed dealer.

–Your state may vary, as well as laws around a private sale–

The lower houses the fire control group (the trigger and the safety) and is where the magazine is inserted, as well as where the buffer tube is mounted. If you are unsure about buying a stripped lower, you can usually find enough variety within the realm of assembled lowers to get what you want. If you are building a “pistol AR” then I highly suggest getting a grip like the Magpul K2, which has a much more ergonomic angle than an old GI grip.

NOTE: The ATF, or BATFE (Bureau of Alcohol, Tobacco, Firearms, and Explosives) ATF for short, is a federal agency, defines and regulates firearms.

The lower receiver is technically “the firearm” itself as defined by the ATF.

Every piece on the lower can be changed out in an endless fashion. Triggers, trigger guards, grips, different buffer weights, magazine releases, ect. The list goes on and on. It’s like adult Lego’s. I’ll stick to the big picture and forgo the details.

Upper Receiver

The Upper receiver is where most of the work happens. There is a charging handle, the bolt carrier group, barrel, muzzle devices, and hand guards. To name the some of the primary components. Just like the lower, there are almost limitless parts and accessories.

Barrels are a hot button topic as they relate to the AR-15 platform. There is no “best” barrel length. Top topic of barrel length is extremely nuanced as it directly relates to the performance of the projectile.(The bullet). There are many factors that alter the performance of the projectile, however I am not going to do a deep dive into all of that. Rather, I want to point out that barrel length should have more to do with YOUR specific needs.

If you live in big sky country and own acres upon acres of land, you might need a 16 or 18 inch barrel, for taking longer distance shots as you protect your stock from predators. If you live in an urban environment and want to use your AR as a home defense rifle, something shorter for working around structures would be better suited to your needs. As shown in the photos. 11.5 inch barrels are very common among AR pistols.

The chamber is the last thing I want to say about barrels. Yes, you can fire a .223 out of a 5.56 barrel. Not the other way around. Unless you have a .223 wylde chamber, which accepts these 2 types of ammunition interchangeably.

There is much more to say about barrels as you continue to learn and research. Chambers, M4 feed ramps, barrel profile, type of coatings. rate of twist. ect. I’m not going to discuss that any further, because it would hijack the article.

Two Adams Arms 16 inch rifles.

Muzzle devices come in a variety of shapes, sizes, and designs. In general you will see flash hiders, muzzle brakes, blast forwarding devices, and suppressors. A muzzle device attaches to the end of the barrel and directs or changes the behavior of expanding the gasses that are propelling the projectile.

Flash hiders, like the common A2 Bird Cage on most military rifles are intended to reduce the bright flash of the expanding gases. Making it harder for enemy troops to see where you are firing from at night.

Muzzle brakes are intended to direct the gases in a manner that increases accuracy and reduces felt recoil. Most of these are audibly louder compared to the other listed devices.

Blast forwarding devices like the Midwest Industries blast can seen in the photos are intended to push the gases forward of the gun. Generally used on shorter barrel lengths to reduce the felt concussion and noise by the shooter and anyone nearby.

Last but not least, suppressors. In order to have a suppressor, you will need to fill out a form with the ATF and pay a tax on it. Suppressors are designed to reduce the audible noise caused by shooting. In general, the reduction of noise has been heavily overstated by Hollywood. If you are shooting a 5.56, the bullet itself is traveling at supersonic speeds breaking the sound barrier like a fighter jet. Although, less dramatically and with a fraction of the generated noise. Still though, shooting 5.56 through a suppressor is not whisper quiet.

Note: Legal designations related to overall and barrel length.

I know, I skipped over the difference between a pistol and a rifle lower. This designation comes in two ways. One, from the upper receiver and namely the barrel. The simplified version, a barrel length of 16 inches or greater, is a rifle. Under 16 inches it must be a pistol or an SBR. Two, whether or not you have a stock or a pistol brace (also called an “arm brace”) on the lower.

The three big designations to know are Rifle, Pistol, and SBR (Short Barreled Rifle). An SBR requires additional paperwork and is more heavily regulated than the other 2. The reason pistols are popular is because you can get a shorter barrel without needing the extra paperwork. An SBR gives you the best of both worlds, a shorter barrel and a stock.

Additionally the ATF does not allow AR Pistols to have a vertical grip (Of 90 degrees perpendicular to the barrel) attached to the hand guard. Another regulation also changed on whether or not a shooter can shoulder fire an arm brace. Yes, you can put the arm brace to your shoulder. Palmetto has information on this and more as well.

On the lower, the buffer tube is mounted to the lower receiver and attaching either a stock or pistol brace will change the designation. By assembling the lower with an Arm brace, you created a pistol lower. If you assemble it with a stock, it is a rifle lower. Once original assembly has been completed, that is now the designation of that specific lower. You can’t put a stock on one day and a brace on the next. Well, physically you can but the ATF regulations do not allow for this.


I think I have covered most of the general information that people ask. I hope that you enjoyed reading this and that you have learned something. Comment below if there is something obvious that should be here in this article.

1st Photos’s parts list:

Adam’s Arms 11.5 Tactical Elite upper.
Lightweight Bolt Carrier Group.
BCM Gunfighter Charging Handle.
Streamlight ProTac HL-X
Muzzle: Midwest Industries blast can.
Magpul ladder rail covers in Olive.
Magpul AFG in foliage.
Scope: Vortex Strikefire II.
Palmetto State Armory complete lower with an SBA3.
Lunar Concepts Splitfix.
Magpul k2 Grip.
Magpul trigger guard. POFUSA Trigger.

I am NOT affiliated with any products, manufacturers, or agencies linked above. This article is NOT LEGAL ADVICE. Laws are subject to change. State, County and local laws may vary.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s