Brownells 75th Anniversary - A Shooting Heritage

Full-size Fun in a Pint-Size Package

Full-size Fun in a Pint-Size Package

Yes, Virginia, You Can Build Your Own AR -15 Pistol

By Rusty Corder

Pint Sized Fun

So you’ve heard a lot about AR-15 pistols, and the bug has bitten you. You want one. Nothing wrong with that. OK, maybe your friends, and no doubt your significant other, will ask, “Why on earth do you want one of those?” You’ll patiently explain that because the pistol is lighter than a rifle, it’s more maneuverable, making it a jim-dandy defensive weapon. You’ll wax eloquently about how the ammo and accessories for the pistol will be interchangeable with your rifles, so expenses for extra gadgets will be kept to a minimum. If you’re lucky, they might even believe you. But no matter what you tell everyone else, we know you want an AR-15 pistol because it’s cool, an attention grabber, and most important, a hell of a lot of fun to shoot.


Since the AR-15 is so modular, why not just grab that old rifle out of the closet, drop a short upper on it and get your pistol? Hold on there, Hoss, it ain’t that easy! According to the National Firearms Act of 1934, if your shootin’ iron started life as a rifle, then it has to stay a rifle. Without getting too deep into the weeds of legal issues, the ATF defines a rifle as having an overall length of at least 26" with a barrel longer than 16". Anything under that is considered a “short-barreled rifle” (SBR), and for one of those, you need to fill out plenty of paperwork and obtain a $200 tax stamp. It’s not as onerous as it sounds, and a lot of folks are doing this, but for now, let’s assume you’re not that patient.

Doesn’t a barrel under 16" make my AR pistol an SBR? Actually, no. It’s not the barrel, but the stock that would cause it to be classified as an SBR. So long as you don’t put a shoulder stock on an AR designated as a pistol, your barrel can be as short as you want and stay safely within the boundaries of the law.

“Alright,” you say, “if I just remove the stock, can I turn my old rifle into a pistol?” Sorry, but no. Remember the law says once a rifle, always a rifle. With AR-15s, whatever the lower was originally built into, rifle or pistol, so it shall stay. Unless, of course, you want to fill out paper work. Wait, there’s more: even though you can’t make your rifle into a pistol, you can turn your pistol into a rifle and then revert it back to a pistol. That’s allowed. Seriously.

To avoid confusion as to what your lower is, you can simply buy a ready-built AR-15 pistol and trick it out however you want. CMMG, a big name in high-quality AR-15s, offers two good examples, the Mk4 PDW and the Mk9 PDW. Both of these pistols are go right out of the box; just add the accessories you want. But if you’re like most of us, you know there’s the easy route and the fun route - you want to build your own pistol. In that case, get a stripped lower, and make sure the seller lists it on the ATF 4473 simply as “Other Firearm” (receiver). Buying a used lower can get a bit dicey if you’re unsure of its pedigree, so if you have any doubts, it’s probably best to launch your build with a virgin lower - they’re not that expensive.

A word of caution here, even though the modularity of the AR allows you to mount a rifle upper and stock on a pistol lower, the pistol upper and the rifle stock must never be on the gun at the same time. That turns it into an SBR. Should the ATF catch you doing that, you will get the pleasure of paying a hefty fine and maybe spending some time at the Iron Bar Hotel.

Roll Out The Barrels

Before starting your build, take a moment to think carefully about what caliber and barrel length you want. If you just want a plinker, you can’t go wrong with a .22 LR or 9mm chambering. Ammo for both is plentiful and inexpensive, and the 9mm has the added benefit of being a good self-defense round. Of course, you can stick to the standard 5.56/.223 chambering, but remember, these rifle-caliber pistols will have more kick, and with that short barrel they’ll have a pretty loud bark, too.

Although 7.5" and 10.5" lengths are common on factory AR pistols, as with so much in the AR world, you can be creative and build your pistol exactly the way you want. Keep in mind, though, that the longer the barrel, the faster and more accurately the bullet will travel. Longer barrels also tend to keep the noise factor down. If you want your pistol chambered in a rifle caliber, you may want to stay above 7.5", with the 10.5" length the sweet spot.

Barrels - Length Chart

Let’s say you want your pistol chambered in the excellent .300 AAC Blackout (BLK) round. CMMG offers a 12.5" barrel that helps maximize velocity to take advantage of the rifle cartridge’s extra punch, while still being compact and keeping the muzzle concussion some distance away from your face. “Mmmmm, nice,” you say, “I like the .300 Blackout, but I really want to keep it compact.” Try the 10.5" Brownells B-TAC (“Brownells Tactical” - get it?) barrel with a “medium” contour that makes it heavy enough to dampen muzzle flip but not so heavy you get a hernia hefting it around.

Want to go smaller? Not a problem! Faxon Firearms is a newish manufacturer that’s building a solid rep for quality - and variety - in its AR barrels. They offer plenty of AR pistol barrels, including a handy 8.5" model chambered for 9mm Luger that’ll get more velocity from the round than any standard 9mm pistol. Still not happy? Orion - another up-and-coming brand we really like- offers a 5" tube, also in 9mm. But if you are dreaming of a really compact AR pistol, why not go for Faxon’s stubby 4.5" 9mm barrel? Of course, calling an AR pistol “compact” is rather like saying a Mare’s Leg Winchester makes an awesome belly gun.

While we’re on the subject of barrels, make sure you pick the right gas tube length for your barrel. Some barrels require a special pistol-length tube, while longer barrels take standard carbine-length tubes. If you are going for a handgun caliber, gas tube length is a non-issue, since these calibers use a direct blow back system.

Buffer Zone

Another part that’s unique to the pistol configuration is the buffer tube, technically called the “receiver extension.” Usually, pistol buffer tubes are thicker than rifle or carbine buffer tubes to physically prevent anybody from slapping a buttstock on the firearm. Even so, you still have options.

Buffer Tube Options
1 Bravo Company:
AR-15 Pistol Receiver Extension Kit
2 Phase 5 Tactical:
AR-15 Pistol Receiver Extension Kit
3 Thordsen Customs:
Enhanced Pistol Cheek Rest Kit
4 SIG Sauer:
SB-15 Pistol Stabilizing Arm Brace
5 KAK Industries:
Shockwave Blade Pistol Stabilizer
6 Law Tactical:
Gen 3-M Folding Stock Adapter

If you live by the KISS principle, you can put on a plain pistol buffer tube like Bravo Company’s. It comes in a kit that includes the pistol buffer, spring, castle nut, and a receiver end plate with a QD sling swivel socket. Nothing else to buy - Q.E.D. You can leave this tube plain, put a brace on it (more on this shortly), or wrap paracord around it for a bit of cushion, as some pistol owners do.

Phase 5 Tactical offers a similar setup, only its tube has a foam rubber sleeve on it for when you hold the buffer tube against your cheek to aid in sighting. Remember, this is a pistol, so ATF rules mean you cannot shoulder it, but supporting it with cheek is kosher. Rules are rules.

If you want extra support while you dance cheek-to-cheek with your pistol, the Thordsen Customs cheek rest is fitted with a saddle that offers a lot more real estate to put your cheek on. This gets your cheek right down on the tube for better stability and a proper sight line.

Cuff ’Em!

Another option for enhancing control of your AR pistol is an arm brace, which essentially turns your arm into a stabilizing platform for the gun. Before we go any further, let’s make a few clarifications about the legality of using a brace. Early on, when the first brace came out, it appeared to be a workaround to the SBR rule, and folks started snugging it to their shoulders like a stock. DO NOT do this! The ATF has since ruled that having a brace on your pistol is legal - its mere presence does not change your pistol into an SBR - but it cannot be used like a stock. Sure, go ahead, think about it, but don’t do it. In the ATF’s eyes, that simple act turns your pistol into an SBR, so why take the chance?

Probably the best-known brace, and one of the first on the market, is the Sig Sauer SB-15 Pistol Stabilizing Arm Brace, which is essentially a soft rubber cuff that fits over your forearm, and cinches in place with a nylon strap. It does what it’s supposed to quite well, though you tend to look like a cyborg with a gun barrel coming out of your arm. Another drawback is that once you have it strapped on, even though it provides extra stability, you basically have one hand out of commission.

As a former bull rider, I have long since flung my craving to be tied to something I can’t get away from in a hurry. That’s where the KAK Industries Shockwave Blade comes in handy. Looking like a ship’s rudder, this brace slips on the buffer tube and its vertical “fin” rests against the inside of your forearm to give you that extra stability. As a bonus, you can also rest the Blade against your cheek for stability and proper sight line.

If you want to take away all temptation of shouldering your pistol, but don’t want to put an arm brace on your new toy, go for a simple sling. Adding a single-point sling to your AR pistol allows you to push the pistol forward, putting tension on the sling and stabilizing the gun when shooting.

Options & Accessories

Even though an AR pistol is much shorter than a rifle or carbine, some of us still want to take a bit more off the length for ultimate ease in transport and storage. The solution? Law Tactical’s Gen 3-M Folding Stock Adapter works as well on an AR pistol with an arm brace as a full-on rifle. Its single-button operation, plus the sturdy locking latch that keeps the stock securely in place when extended, is just the ticket. But again, don’t take this as an excuse to put a stock on your pistol.

Speaking of things you can’t add to your AR also can’t put a vertical grip on the forend. Mounting one of these to your pistol magically turns it into the ATF’s AOW (Any Other Weapon) classification and can earn you a one-on-one visit from your local ATF agent. If you really need something on the forend to aid with pointability and muzzle control, go ahead and mount a hand stop on the forend; the ATF won’t mind a bit.

AR pistols make great car guns, self-defense weapons, and of course, plinkers. They are also a viable alternative to an SBR, and you won’t have to endure the extra expense and the added wait time. If you do decide someday to go for a short barreled rifle, your pistol already has you are more than half way there. Beyond the fun factor, another benefit of an AR pistol is that it is compact enough to fit into an overnight bag or backpack, and it’s covered by your concealed carry pistol permit. As with all responsible firearm ownership, be sure you are in compliance with your local, state, and federal laws regarding ownership of an AR pistol. Once all that’s square, get out there and start punching some holes in targets!