Some Options for AR Pistols, by Legal Eagle

Several years ago, I ran across an article on the versatility of the .300 AAC Blackout round. One of my hobbies is hand loading ammunition. The adaptability of the cartridge was interesting. In the summer my wife and I live near Yellowstone on the Wyoming-Montana border. We often enjoy camping and fishing in the area I grew up in. We don’t have an RV, just a tent and cots. Nothing fancy just as my father and I camped in the sixties. Most of our favorite spots are remote and I had been looking for a firearm that was more than a heavy revolver, but less cumbersome than a rifle or shotgun capable of rapid follow up shots.

Some sources listed the velocities out of a ten-inch .300 Blackout barrel of a 110-grain projectile at 2,200 feet per second. A 150-grain bullet with the proper propellants could be boosted to 1,700 FPS out of the same barrel. A hot .357 magnum out of an eight-inch barrel can launch a 158-grain hard cast bullet as much as 1,500 FPS. There are several people I know who carry either .357 magnum revolvers, but with four-to-six-inch barrels, or .44 magnum revolvers. Several of my friends now pack a 10mm in the backcountry. Unless you have nerves of steel and perfect shot placement none of these will stop a charging grizzly. Growing up, I remember hearing stories of the big bears failing to stop their charge after several hits from a .30-06. So, I realized the limitations of the .300 Blackout cartridge also in stopping such a tough animal. Unfortunately, I do not have nerves of steel nor am I capable of perfect shot placement under stress.

However, in all my time in the woods, and seeing plenty of bears, I’ve never been attacked by a wild animal. Still, it seemed prudent to have a firearm with some punch that would be easy to make hits with and compact. A firearm able to quickly bring on target. A .300 AAC Blackout pistol with a red dot and Picatinny rail mounting a light would be just the ticket, I reasoned.

Like most people I can shoot more accurately with a rifle. An AR pistol with a brace is not a rifle but it does give at least three points of contact when used as intended. I bought a stripped lower receiver from my local gun shop and ordered a lower build kit from Palmetto State Armory. Online an upper receiver with a ten-inch barrel was ordered. Besides a red dot optic and flashlight, a detachable sling was desired. An SBA3 pistol brace was chosen because of the good reviews and the ambidextrous QD sling socket. After everything was assembled it became one of my favorite firearms. Accurate, low profile, in a caliber that had dozens of projectiles in weight and configuration with many suitable propellants that could be experimented with. But then came January of 2023.

The ATF rule 2021R-08F, almost 300 pages of nebulous wording of what classifies as a short-barreled rifle (SBR) includes overall length, weight, and eye relief of an optic. What it boils down to is if you have a barrel less than sixteen inches and a pistol brace the ATF now considers it an SBR.

Our options, assuming that this revised ruling will actually become “law” on June 1st, 2023 will be any of the following:

  • Remove the brace.
  • Surrender the firearm to an ATF office.
  • Destroy it.
  • Amnesty register it, as an SBR.
  • Install a barrel of at least 16 inches. (Or, weld on a barrel extension of some sort, making it 16″ or longer)

The latter which I ultimately decided to do. Keep in mind that once your lower receiver has a rifle upper on it or you decide to install a rifle barrel it is forever a rifle in the eyes of the ATF. There is no going back.

I decided not to take advantage of the pistol brace amnesty period from January 31st until May 31st. The two-hundred-dollar fee will be waived for the tax stamp, and you will wind up with an NFA weapon. There were several reasons I was advised not to do this. For me, the most important consideration was not being able to cross the state line without having to get prior permission from the federal government, a requirement when traveling with an NFA item. This would not only be troublesome living near a state line, but I wondered how long would it take to obtain permission once the paperwork was submitted. We seldom plan that far ahead in the summer.

As I write this in early May of 2023 not only are lawsuits opposing the pistol brace ban in play but, if I understand correctly, a U.S. House committee voted to nullify the pistol brace rule. Now it goes to the House of Representatives, there is a good chance that it will pass there also. From there it goes to the Senate, it is doubtful that the Senate will vote to nullify the pistol brace rule, but if they do and it ends up in Joe Biden’s hands. We all know what he will decide.

Initially, I decided to remove the brace. A short pistol buffer tube was installed. This seemed awkward, with the pistol brace the firearm could quickly be raised and a cheek weld acquired between upper bicep and cheek without touching the shoulder, giving four points of contact. It was my thinking that it might be possible to make some light-plinking loads with pistol and shotgun powders and still get a cheek weld on the foam-covered buffer tube without putting your eye out. Five 110-grain rounds were loaded with the max permissible grains of each for 115 grain 9mm. These were loaded with small pistol primers because of the low pressure anticipated in the Blackouts much more voluminous case.

A Magpul 7.62×35 magazine designed for 300 Blackout had been purchased I was curious if it would reliably feed rounds with different weight projectiles and at 100 yards how close they would group. (Later after twice pacing off the distance it was found that what I had always thought was 100 yards was really 84.) Seven full power rounds ranging from 110-grain Barnes loaded with 19 grains of Hodgdon LIL’GUN to factory Remington 220 grain subsonic were dug out of the ammo locker.

A 13-inch by 10-inch paper platter was glued to our plywood backstop with a black magic marker dot in the middle.

The five pistol rounds were loaded one at a time into a .223 magazine. The purpose was to see if they would cycle the bolt far enough to lock open on an empty magazine. Wearing eye and ear protection, my youngest son and I took turns firing the five light loads. The only round that generated enough pressure to eject the empty casing was the one loaded with HP-38; it did not lock the bolt open on the empty magazine though. None of these loads had any significant recoil.

The PMAG was loaded save for the last seven intended for the target. In reverse order starting with the 220-grain subsonic were then loaded. Once again, we alternated shots. Taking turns running up to the target to mark it after each round was fired. Surprisingly all except for 4 and 5, clean shot and the ancient HS-5 of uncertain vintage, grouped in the lower right-hand corner. We discovered that if forced to use a grab bag of a different mix of powders and projectiles of various weights for self-defense against man or beast in a survival situation the point of impact would be nearly the same at realistic defense distances.

Two days prior, when the brace was still attached, we were hitting water-filled soda bottles at the same distance (84 yards) and at the same informal shooting range. The same red dot sight was still mounted on the rail. My only explanation of the lower right-hand grouping was the different perspective, parallax, without the wide SBA3 for a comfortable brace and cheek weld. It seemed unlikely that changing the buffer tube was the cause. The 300 BLK PMAG handled all the different projectile weights without a problem.

My son was an active duty U.S. Marine from 2005 to 2010, so he became used to living with an M4 or M16 during Iraq deployments and was comfortably familiar with Eugene Stoner’s design. In his opinion without the brace the AR pistol was good only for casual plinking, we both found it difficult without using the magazine as a monopod to hold the pistol steady on target. For me, it was clearly not useful for its intended purpose. My goal now was to find a way to keep shooting the BLK without spending too much money. I found a 16-inch .300 AAC Blackout barrel with a pistol gas port on ‘Right To Bear.’ An online company I had never heard of. For $95 including shipping. A new barrel arrived promptly in just a few days.

Before getting into the installation, I would like to explain why you might want to invest in the .300 Blackout. First, it is no longer an uncommon round, it can be found in most places. A longer barrel life is expected with most common loads. If you already own an AR-15 a new barrel or easier yet a new upper is all that is needed. It is a great suppressed round. It offers good performance out of shorter barrels, unlike the .223 or 5.56. It’s a good woods gun for game up to deer size. Most common BLK rounds feed fine out of the .223 magazines you already have.

MagPul makes a PMAG designed specifically for the 300 BLK which handled the heavy projectiles fine. If you reload it is inexpensive to shoot. A used single stage press can be had for as little as $50 on eBay, a good investment for a shooter. I read somewhere that there is around 400 different .308, 7.62 mm and suitable .309 caliber projectiles in different configurations, HPBT, SST, Core-lokt, Power-point, Ballistic-Tip etc. Worldwide.

I don’t think there will ever be a time when thirty caliber rounds of some type cannot be bought, scavenged or cannibalized. The Blackout will never be a 300 Winchester magnum but the 150-grain bullet from a 300 Win Mag can be pulled and sent out of a sixteen-inch barrel at 2,000 FPS or more, some loads with double base powder push the same weight projectile to almost 2,500 fps. The cost for range rounds can be inexpensive. I’ve bought a lot of surplus 147 and 150 grain jacketed projectiles for modest sums. Rim Rock bullets in Polson, Montana have 115 gr. RN hard cast .308 bullets at five hundred for $40 as I write this. Everything from 110 grain surplus .30 caliber carbine bullets to 240-grain thumpers have been fired from the Blackout. I know of no other cartridge that gives you a wider range of propellants and projectiles that can be used. An important consideration in situations of restrictions or shortages of ammunition. With a bullet mold suitable lead projectiles could be fabricated, something much more difficult for the higher velocity 223 or 5.56 where unjacketed projectiles must be hardened to a Brinell hardness of more than 16.

Some low-pressure rounds have been loaded with small pistol primers, as I did with the first five lightly loaded rounds. Small rifle and small pistol primers are the same size. Small rifle primers are made of a slightly thicker material. I am not advocating you use small pistol primers, especially at pressures over 35,000 PSI. Always use small rifle primers in the .300 Blackout, especially if in doubt as to the pressure. Some BLK rounds exceed 62,000 PSI.

One more advantage is it seems that most pistols and shotgun powders have been experimented with and still are by reloaders. Often a recipe for someone’s new favorite load can be found online. The difference in velocity between a nine-or ten-inch barrel to a 16-inch barrel is usually only 200 to 250 fps but for a 150-grain bullet the difference is 919 ft lbs to 1,154 ft lbs of energy which is not insignificant so there is an advantage to a longer barrel.

In addition, Blackout cases can be easily fabricated from plentiful 223 or 5.56 cases. Even with simple tools it is possible. I make a mark just below the neck of a 223 case at 1.37 inches or a smidgen above. Place the case in a shell holder. Place the shell holder at the bottom of the jaws of your vise so your mark is even with the blade of your tubing cutter. Holding pressure with the finger of one hand rotate the cutter around the case with the other while gradually turning the cutting knob. The first couple of rounds you will probably ruin. After that you’ll get the hang of it. Using the outside of the deburring tool I trim the case to 1.368 inches. In practice I’ve found anything between 1.36 and 1.37 is fine.

Use the inside burring tool to smooth the inside of the case mouth. Now run the lubricated case through the de-priming resizing die. Leave the de-priming rod in so that the inside of the case will form smoothly around the ball. When case lube cannot be found coconut oil makes a good, but messy substitute.

Installing the barrel in the upper receiver was uncomplicated but not as simple as anticipated. The tools needed were a torque wrench, gas tube alignment tool or piece of .18 inch tubing or rod. A barrel nut wrench and a copper-based anti-seize compound. An upper receiver action block was ordered on Amazon for $10. I planned on using the same gas block and gas tube to save on expenses. If there is a gunsmith near you, for a few dollars he can check the headspace of your new barrel. Saving you the cost of purchasing the Go and No-Go gauges.

After removing the hand guard, the upper receiver was inserted into the action block and secured in the vise. It was necessary to use a C-clamp on the upper outside of the block to keep it from spreading. A heat gun was used to heat the flash suppressor, after a short time the loc-tite softened and it was removed. Next, the gas block and gas tube were removed. The first snag came when I attempted to remove the barrel nut. Using the barrel nut wrench I could not get it to budge. I thought these were torqued to 35 pounds, was this thing put on with Loc-Tite or had the factory forgot to coat the threads with an anti-seize compound? I wondered. Using the heat gun, the barrel nut was heated, still it refused to budge. When my son came home, he attempted to remove it with no luck. We resorted to me holding the barrel nut wrench and him using a hammer on the end of the wrench, after heating it once again it finally came loose with some careful hammering on the end of the wrench.

The final headache was getting everything aligned and tightened down. Anti-seize was applied and the new barrel and nut went on easily. Tightening the nut and aligning the gas tube so that it passed through the barrel nut, upper receiver and entered the gas key exactly centered was more difficult than anticipated. After an hour we were at last successful. Our AR pistol had a free float barrel if you have the front sight gas block and heat shield type there is a good tutorial at The NRA’s also has an excellent article.

After everything was put back together an inexpensive 3X magnifier was added to celebrate its new status as a rifle. We took it out the next day and put fifty rounds through the new rifle without any problems. I went the cheap route using all the old parts except for the crush washer. So, the rifle looks a bit unconventional with the abbreviated heat shield/hand guard and pistol brace. Without wearing a winter coat, (a usual item of clothing for much of the year in this part of the country) it would be nice if the ‘’Brace’’ could extend another half inch or so. But the pistol-become-rifle is more than serviceable and legally, nothing stops me from installing any standard rifle stock now. All in all, for a little over a hundred dollars, we both felt it was a good option to comply with the upcoming pistol brace rule.