SBR versus AR pistol question

[RevolverRob]

FYI that's no longer the case as of a couple years ago. Now a lower receiver with a stock or pistol buffer tube installed is still to be considered a receiver.

Huh, I didn't realize there was a change, but I see there are apparently a few ATF Tech letters out now to that effect. It also implies that removing a stock and stock buffer tube from a lower allows it to be used as a pistol lower.

[Gray222]

If you've bought a loose unassembled lower, do you have any way of knowing if it's listed as a pistol or rifle lower?

What makes a bare lower into one or the other?

You can still find "pistol" marked lowers and when you get them sent to your FFL / or when you buy an AR15 lower from an FFL just register it as a pistol.

A pistol marked lower is unnecessary but if thats your reasoning for purchasing it then it may work for you.

[STI]

There is a "Type" section the 4473 (Section D, Question 27) which is completed by the Transferer/Seller - The ATF says (from the instructions on form 4473):

So a bare AR15 receiver can be (SHOULD BE) listed as a "receiver" or "frame" on the 4473 (either was fine with my ATF inspector, when I sold guns). Note that if a lower receiver was assembled with a stock it was designated a rifle. If it had a pistol buffer tube installed it was designated a pistol. If there was no buffer tube, but there was an LPK installed it was still a receiver or frame.


The installation of a stock, installation of a shoulder stock makes a lower receiver a "rifle" receiver. And generally according to the ATF removal of the stock does NOT convert the receiver back. But this is pretty damn gray, because according to the ATF, installing a 16" barrel in a pistol and then attaching a stock (in that order) is a legal rifle conversion. But converting "pistol" AR into a rifle AR and back again, is/is not legal? Depends on the damn time of day and the wind, it seems.

My opinion (IANAL) - If one has a receiver that is serialized and stamped SBR you avoid this problem. If you have a bare receiver, turn it into a rifle or a pistol. If you go rifle, it stays rifle, unless you SBR it. If you go pistol, it stays a pistol, unless you SBR it. - It's just easier that way.

You can still find "pistol" marked lowers and when you get them sent to your FFL / or when you buy an AR15 lower from an FFL just register it as a pistol.

A pistol marked lower is unnecessary but if thats your reasoning for purchasing it then it may work for you.

It's a bare Ballistic Advantage lower, no buffer tube or stock, came with no LPK. Now has LaRue MBT and mil spec pins and mag catch. I assume I could build it up to be either a rifle or pistol at this point so long as I don't waffle around after it's configuration is finalized.

Original plan, that I have barrel and bolt for, was hunting capable 18" 6.8SPC SPR-ish clone. Now indecisive me would rather have a Glock mag 9mm AR pistol.

[ReverendMeat]

It's a bare Ballistic Advantage lower, no buffer tube or stock, came with no LPK. Now has LaRue MBT and mil spec pins and mag catch. I assume I could build it up to be either a rifle or pistol at this point so long as I don't waffle around after it's configuration is finalized.

Original plan, that I have barrel and bolt for, was hunting capable 18" 6.8SPC SPR-ish clone. Now indecisive me would rather have a Glock mag 9mm AR pistol.

You can do whatever you like with the receiver as it was sold to you as a "receiver" or "frame" (provided the FFL that transferred it to you isn't stupid and recorded it properly). If you configure it first as a pistol you can later turn it into a rifle and back to a pistol again if you wanted. However if you configure it first as a rifle it must stay a rifle. Obviously you could always say that you built the receiver into a pistol first regardless and I don't see any way anyone could prove otherwise. But that would, of course, be illegal.

[RevolverRob]

Now indecisive me would rather have a Glock mag 9mm AR pistol.

It may be an unpopular opinion, but I'll share it, since you brought this up. Having done up a few 9mm ARs now (4 to be exact, including one 9mm Glock AR that never worked right). The Glock 9mm AR guns are a solution in search of a problem. That "problem" is cheap mags and laziness on the part of folks who want a 9mm AR, but don't want to buy Colt-pattern SMG magazines. The Glock receiver guns have come a long way from the initial ones, but still suffer from the worst problem a 9mm blowback "squirt gun" can suffer from - single-feed magazines.

Single-feed magazines in SMGs are generally a no-no, and especially in blowback operated guns (like the Colt pattern). The only exception to this I can think of appears to be the Kriss Vector, which was designed ground-up to use Glock mags, and is a locked-breech type operation, not a blowback gun. In the history of SMGs, single-feed mags were quickly replaced by double-feed magazines (true "double stack" magazines). For instance, the STEN is a simple gun and works okay(ish), but the single-feed magazines are a weakness that frequently fail. Refining that platform, with a double-feed magazine, and better made bolt in the form of the Sterling SMG makes it one of the most reliable SMGs on the planet.

Colt "solved" the problems of making a 9mm AR run as a blowback squirt gun in the 1980s. And in my opinion, it's best to not muck with their "solution". Which is a dedicated magazine block, a narrow hammer installed into a standard AR15 trigger group, a large ejector, a heavy buffer installed, and a proper double column stick magazine. When quality magazines (Metalform, Colt, ASC, C-Products - in that order) are used guns are generally 100% reliable and work very - very - well.

The Glock-mag fed guns, really need a ramped barrel and bolt, and sometimes fitting between the upper and lower to work well. If you have a non-dedicated lower, you're going to spend A LOT of time fiddling with the magazine block to get it to run properly. The dedicated lowers are angling the magazine well now to get a "straighter" shot in terms of feeding from the Glock magazine. By contrast if you drop in a Colt or Hahn Precision (my personal choice) dedicated magazine block, throw in a 9mm hammer and BCG, and a heavy buffer, you'll be shooting reliably in an hour.

In short, if you want to do a 9mm AR on a non-dedicated lower - built a Colt-Pattern gun. If you want to do a 9mm Glock AR - buy a dedicated lower, ramped barrel, ramped bolt, and build it up in that way.

[STI]

In short, if you want to do a 9mm AR on a non-dedicated lower - built a Colt-Pattern gun. If you want to do a 9mm Glock AR - buy a dedicated lower, ramped barrel, ramped bolt, and build it up in that way.

You're right. After more research I agree, and shouldn't have mentioned using my standard AR15 lower potentially being a home for a Glock mag gun. There's lots of issues beyond what you mentioned as well.

Sorry all for the diversion from the OP.

[ReverendMeat]

Single-feed magazines in SMGs are generally a no-no, and especially in blowback operated guns (like the Colt pattern). The only exception to this I can think of appears to be the Kriss Vector, which was designed ground-up to use Glock mags, and is a locked-breech type operation, not a blowback gun.

The Kriss is blowback, not locked breech. I'm not tracking how either method of operation would make a difference when it comes to magazine reliability?

[RevolverRob]

The Kriss is blowback, not locked breech. I'm not tracking how either method of operation would make a difference when it comes to magazine reliability?

By technical definition the Kriss is a lever-type action delayed blowback vs. closed bolt blowback of the Colt (which is driven strictly by spring pressure).

The original challenge the double-feed (true double column) mag, overcame was two-fold. 1) A weaker magazine spring (easier to load) could push bullets up to be chambered by an open bolt gun, 2) Magazine feed "lips" of double-column guns are less precise and allow for sloppier feeding that a high-rate of fire gun wants/needs. - This in turn allows guns to be built to a cruder set of specifications.

The Colt SMG fires from a closed bolt and on fully automatic uses that "sloppier feed" provided by a double column mag to keep things running well. It turns out, with a double-feed magazine you simply get a larger feed ramp area which tends to result in less feed-related malfunctions (unless the mag spring/follower is no good).

The Kriss was designed around the Glock magazine, including the feed angle and with the action mechanism that is more precisely fitted into the chassis of the gun. The Colt was designed around an almost straight shot feed with a wide feed ramp, in this scenario a double column magazine simply works better.

There are several open bolt designs out there that feed fine from single-feed mags, but again they were designed around those magazines.

[DMF13]

The Glock 9mm AR guns are a solution in search of a problem. That "problem" is cheap mags and laziness on the part of folks who want a 9mm AR, but don't want to buy Colt-pattern SMG magazines.

Well, to be fair, some folks, like friends in Colorado, can't buy "Colt" 9mm mags, since they aren't allowed to buy any mags with a capacity of more than 15 rounds, after June of 2013. It's my understanding that all the "Colt" 9mm AR mags hold more than 15 rounds. So if they want a 9mm AR, then they can't run out and start buying a "Colt" pattern AR.

However, I want a "Glock" 9mm AR, because of laziness, and the plethora of 9mm Glock mags I have lying around.

[CleverNickname]

I have a lower that has been engraved as an SBR but I want to be able to travel with it unencumbered by having to notify the ATF everytime I go out of state. Can I remove the adjustable buffer tube and replace it with a pistol buffer tube and add a brace, or should I purchase a new lower and add the pistol components to that?

You could do that, but you wouldn't accomplish what you're trying to do. SBRs don't have to have stocks.