AR-15s

Throwback Thursday: How to Legally Build an AR Pistol

There’s nothing better than shooting a sleek, powerful AR pistol… except shooting one that you build with all your favorite custom parts. So, why doesn’t everybody jump on board the pistol-building express? One word: Feds. But, with a little finesse and a lot of knowledge about your local gun laws, you too can confidently build a classy AR pistol.

Note: This article is for educational purposes only; it is not meant to be construed as legal advice. You are ultimately responsible for your own actions and we advise you to seek guidance from a legal professional in your area before attempting any AR pistol build.

Why choose an AR pistol?

The first question you may be asking is, “Why choose an AR pistol over a standard rifle?” My initial response would be, “Why not both?” But, in all seriousness, an AR pistol provides you with more maneuverability, especially in tight spaces, and depending on your configuration, can give you most of what a standard AR-15 carbine does. Additionally, if you plan to run a suppressor, the shorter barrel will give you a similar overall length to a rifle.

Distressed AR 15 pistol Ammunition, Magazine .223 556
Gone are the days of just some slight padding on your buffer tube. Feel free to add in your choice of pistol stabilizing brace!

Drawbacks

Although an AR pistol can be more lightweight and maneuverable, there are some drawbacks. Because you have a shorter barrel, you’re going to get less velocity out of your caliber of choice. This is more of an issue for some, rather than others. For instance, the lightweight bullets in 5.56 NATO derive most of their power from velocity, however, the .300 AAC Blackout was purpose-designed for shorter barrels. Do some research on your intended caliber and see what barrel length works best for you.

Additionally, an AR pistol will have more muzzle blast, concussion, and felt recoil than a comparable rifle. This is most noticeable indoors and is a factor you should consider depending on where you shoot and your intended purpose for the firearm.

AR Pistol Laws and Definitions

The first thing to note about any custom build to make sure you stay safely within the law of your local and state gun regulations. Call your local FFL. They should be able to get you that information pretty easily. As a general rule though, a short-barreled rifle classification is what you want to avoid. How are those classified? A rifle with less than a 16-inch barrel or an overall length of less than 26 inches will get you that unwanted $200 NFA (National Firearms Act) tax. Additionally, per ATF guidelines, AR pistols equipped with braces may not have a length of pull longer than 13.5 inches — in other words, at full extension, the distance between the trigger and the rear edge of the brace cannot exceed 13.5 inches.

Another important note is how the BATFE (Bureau of Alcohol, Tobacco, Firearms, and Explosives) defines a rifle vs. pistol. In short, a rifle is anything with a stock that you fire from your shoulder. The ATF defines a pistol as “…a weapon originally designed, made, and intended to fire a projectile (bullet) from one or more barrels when held in one hand, and having: a chamber(s) as an integral part(s) of, or permanently aligned with, the bore(s); and a short stock designed to be gripped by one hand at an angle to and extending below the line of the bore(s).” But, hang on. I’ve seen tons of AR pistols that look almost identical to an AR rifle. What gives? And how are they avoiding the NFA tax? The answer? Pistol braces.

AR Pistol
An AR pistol is a great compact alternative to a longer AR-15 rifle.

Bracing for Impact

In an open letter to the BATFE, the question was posed whether a brace, which traditionally has hand-holds or arm straps to help the shooter stabilize their shot while firing with one hand (fitting our pistol definition), would still classify the firearm as a pistol even if the shooter “happened” to “accidentally” place the end of the brace on his shoulder. Initially, their answer stated that this type of shouldering would qualify the weapon as an SBR under the NFA. In 2017, however, that statement was amended to read as follows:

“With respect to stabilizing braces, ATF has concluded that attaching the brace to a handgun as a forearm brace does not ‘make’ a short-barreled firearm because… it is not intended to be and cannot comfortably be fired from the shoulder… Therefore, an NFA firearm has not necessarily been made when the device is not re-configured for use as a shoulder stock — even if the attached firearm happens to be fired from the shoulder.”

So, if you’re looking to add that extra stabilization to your build with a brace, the BATFE has given the green light.

Maxim Defense CQB AR Pistol Brace
Adding an AR pistol brace gives you similar benefits to a stock, but doesn’t require additional legal paperwork.

Keeping Your Weapon Legal

The main thing to ensuring your build is legal is to keep it under the “pistol” definition. Here’s how:

  1. Use a stripped lower receiver that has never been barreled as a rifle action. Or a receiver that started out as a pistol in the first place. If the receiver started out as a rifle and was classified as a rifle, you’re in trouble. Interestingly enough, if the receiver started as a pistol, you can strip it, convert it to a rifle and then back to a pistol without a problem.
  2. Use an angled foregrip such as the Magpul AFG that is less than 26 inches from the unadorned tip of the barrel to the end of the buffer tube. A vertical foregrip is not allowed on a pistol.
  3. Stay under the 16-inch barrel length and 26-inch overall length.

Really, if you follow these guidelines along with your local laws, building a legal AR pistol is a piece of cake. Now, since I know you’re wondering, here are some of my favorite components when building my ARs.

Magpul AFG2 AR-15 Grip
Be sure to use an angled foregrip such as this Magpul AFG2, because you cannot use a vertical grip on a pistol without reclassifying the firearm as a short-barrel rifle.

My Go-To Components

If you’re anything like me, you’ve got an ideal product for every square inch of your custom gun. But, just in case you’re in the market for some killer ideas, here are some of my top choices for custom builds:

Whatever parts you choose to build your perfect AR pistol, have fun with it and be sure to keep it legal with the above tips.

Have you legally built an AR pistol? How did it turn out? What’s your favorite barrel length, caliber, and setup? Let us know in the comment section!

Editor’s note: This post was originally published in September of 2020. It has been revamped and updated for accuracy and clarity.

About the Author:

Richard Douglas

Richard Douglas is a firearms expert and educator. His work has appeared on large publications like The National Interest, Daily Caller, American Shooting Journal, and more. In his free time, he reviews optics on his Scopes Field blog.
The Mission of Cheaper Than Dirt!'s blog, The Shooter's Log, is to provide information—not opinions—to our customers and the shooting community. We want you, our readers, to be able to make informed decisions. The information provided here does not represent the views of Cheaper Than Dirt!

Comments (23)

  1. Patrick Sweeney has a good instructional book on the AR15. It is full of pictures and “tips.” It’s a soft cover magazine size about 50 pages. I found another excellent step-by-step book online. There are several out there. YouTube is fine, but I like to have a manual at my fingertips. One curious thing I found is how the experts disagree on how many ft/lb of torque to apply to the barrel nut. I guess it’s not that particular, maybe? You’ll see. God bless and stay safe.

  2. In Maryland, you do not need to claim your stripped lower as a pistol or rifle. I specifically asked that question to my FFL and they clearly stated that you do not. not sure if this changes state to state, however.

  3. Ten inch 9mm Anderson upper paired withFM 9 mm glock style lower shockwave blade brace. Real handy little “ pistol “

  4. Before you build an AR pistol, please for your sake read completely the NEW rules that are being proposed. A number of changes will make many AR 15 platform pistols into SBR’s. Look at the work sheets that will be used to clarify the components in the build. Not law yet but I doubt if much will change prior to the publishing date. Find out for yourself, do not become a felon by accident.

  5. You can use a vertical grip (VFG) on a non-pistol & non-rifle (aka ‘other’) receiver as long as your overall length is >=26″. This is common in states with assault weapon bans as the evil feature rules only apply to rifles, and AR pistols tend to be banned.

  6. I used a kit I bought online (Very, very reasonable when On Sale). It has a mil-spec carbine style foreend, so no free-float. I truly believe that with sights or a red dot you don’t need free-float accuracy. Their stabilizing brace is very simple, which is what I like. My advice on any AR is to get rid of that useless flash suppressor! It’s loud and adds unneeded weight, especially on a pistol. When you remove it, you will probably find that the barrel crown is saw-cut. Here’s your chance to improve accuracy by recrowning that muzzle. Note: On a rifle, that muzzle device might be part of your 16″ legal length. If so, it will be very difficult to remove and illegal to do so. God bless and stay safe.

  7. I am new to building my own weapons. I’ve been wanting to do it for years as a hobby. My question is, Where would be a good place to start on learning about Uppers, Lowers and just basic parts needed to build a pistol or riffle? What parts of the weapon has to be changed in order to covert it from semi to full auto? Is it more feasible to make your own ammo, and how does the “grain” of the ammo affect the outcome?

  8. NO! NO! NO! A receiver when purchased is an other on the 4473. Complete or stripped its an other. At least federally. It fits the definition of neither a pistol or a rifle so its an other.

  9. in missouri alternative deear season i can use a ar pistol as long as it stays under 26 inches. How long of a barreled upper for a 6.5 grendel can i get while using a buffer tube to stay 25 inches or a hair under.

  10. Funny how Jon B said an idiot did that.
    I actually lived in the little town where that bump stock was made.
    It was great for the town as there just is no jobs there to speak of.
    Like I said I lived there many years ago. I was a teenager when I moved but looking on line
    I still remember many of the family names.
    The guy who owns the factory for the bump stocks is by family name the same as a guy
    who drove the school buss I rode.
    Funny how the bump stock was just an easy way to do something that you can actually do
    without the bump stock.
    I’m not a gun enthusiast at all but I do own some.
    Most are inherited and I do not use them or play with them. I just own them.
    I do own two rifles and one shot gun I used to hunt when I was a kid when we hunted to eat.
    Yes I am that old.
    I am a supporter of the 2nd amendment but I don’t understand people who love guns and just
    eat sleep and what ever guns.
    I have a concealed carry I have a couple of others at home for defense but seldom ever shoot them.
    I live where I can shoot any time, day or night on my property but I don’t fire more than maybe eight or ten rounds a year.
    I have a weapon than can be bump shot and would never put a bump stock on it.
    In Vietnam I never carried my weapon on full auto and I don’t think I ever shot it in full auto.
    Mostly it’s a waste of ammo. Bush rattles or wiggles usually meant eight or ten men emptying a clip on full. I only fired if I had a clear target. EVER!
    Did I ever hit or kill a man? I truly do not know. I never ran over to see if there was a body there to check vital signs on.
    I just had to throw this ramble in because of how funny I think bump stocks are. Or in other words how silly I think they are. Silly like open carry but I support your right to both

  11. You forgot one very important part. You must register the lower as a pistol when you fill out your 4473. If you do not, the feds, in theory, can charge you with making a handgun out of a rifle. Also remember to warn people not to use vertical forearms. Putting a vertical forearm on a pistol is a federal crime. Yours respectfully, Steven Howard Attorney at Law

  12. Yes, the LV shooting, made the ATF change how they judge length of rifle. If you are able to look at fbi files, you will see, that it wasn’t the guy the news told you it was. He was there to sell those weapons, and had a ghost email setup to email himself and others so the fbi wouldn’t catch wind. He said, you have to try so and so weapons. Why would you email yourself that question? Lot’s of other things in the fbi files. Anyhoo, back to topic. I personally would not have bought a bump stock, but I do enjoy AR pistols. So, the ATF rule change benefited me, and others that I know. So out of a bad thing, came a some what decent thing. Made ar pistols go from a sbr to a pistol.

  13. I put one together about a year ago — Anderson stripped lower and a “slick” upper, KAK Shockwave Blade stabilizer, 10 1/2″ barrel, “fowarder” type blast can, 7″ M-lock handguard, AFG 2 foregrip. Nice, fun shooting gun.

  14. If you’re anything like me, you’ve got an ideal product for every square inch of your custom gun. But, just in case you’re in the market for some killer ideas, here are some of my top choices for custom builds:
    – Black Rain Ordnance AR15 Complete Lower Parts Kit Enhanced Version Magpul MOE Pistol Grip/BRO Drop In Trigger
    – CMMG AR-15 Complete Lower Parts Kit

    This list has some nice ideas, but have two lower parts kits does leave us novices floundering for a quality Heavy / Light (pistol length) barrel. No judgement – just sayin.

  15. I j just finished building 2 AR pistols, 10.5″ barrels, one in 5,56, the other in ,300 AAC Blackout, Sweet isn’t the word for them. I didn’t use what could be termed “premium” parts, but each build topped out at about $650 apiece. Search all the websites for deals on the parts you want and you can avoid the steep prices of ready made builds. The .300 is now my Home defense weapon; 225 gr subsonic works with my pistol length gas system pretty well w/o a suppressor, but I do have a muzzle brake/compensator that with this ammo has a significant reduction in noise/recoil. The 5.56 I actually paired with a Polymer80 OD lower that came as a non-FFL kit that I had to mill, but no difference in operation or ammo moving through the tube. Both very accurate out to 200 m. Strongly recommend Pat Sweeny’s book, “Building Performance Ar’s” as a guide to different builds, calibers, barrel lengths. Main thing is buffer weight married to gas tube length.

  16. Two things:

    1 you don’t need a Magpul AFG to have a pistol but you can use one if you want.

    2 the barrel on a pistol can be as long or as short as you want. There is no limit.

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