Ar pistol build laws

andy41567 · Dec 17, 2019

I am building my first AR pistol in 300blk. I have done a bunch of research and think I have interpreted the laws and rules correctly. But I wanted to ask to be sure to some of the more experienced guys.

I purchased my lower from my Gunsmith and on my 4473 block 18 it is marked "other"

I am going run a 9" solgw 1.7 twist barrel with a spikes barking spider comp. Eventually I'll run it suppressed. Pistol length gas system of course.

I bought an SBA3 brace with the buffer tube.

Now if I understand correctly I need to make sure i am at 26" and over or is it 26" and under?

Now I know not to run a Foregrip! But I can run a hand stop or wedge... Like the magpul or BCM... Correct.

Now as for the Brace it is adjustable but is not a stock. But if I understand correctly and according to the ATF you ARE now allowed to shoulder a pistol AR. Did I read that correctly?

The only technical question I had was... What buffer spring and weight to run/start with? I plan to use subs and supers and also know that the spikes comp will add some back pressure.

Did I miss anything?

mvee · Dec 17, 2019

There is no minimum size for a pistol.

SkiPatrolDude · Dec 17, 2019

You can shoulder your pistol brace without fear of committing a crime.

No length requirement for pistols.

Standard carbine buffer and spring should work fine. If you want a tuned set up, consider a Superlative Arms Adjustable Gas Block. This will allow you to fine tune recoil, ejection, and reliability, while not having to mess with buffer weights and springs as much. This will be especially helpful when you begin running this suppressed.

smokey · Dec 17, 2019

the 26" thing is only an issue if you run a VFG. In that case, you need to abide by the new measurement guidance by the atf and be over 26". I'd just skip that whole issue and run a hand-stop only(although the afg's are fine).

Biggfoot44 · Dec 17, 2019

What Smokey said ........... Until ATF Advisory Letter V 3.0 is released .

andy41567 · Dec 17, 2019

very good guys. thanks.
i have an SLR adjustable gas block. Guess i will throw that on their instead of the fixed SLR i got for it.

danb · Dec 17, 2019

definitely use the adjustable gas.

I'd start with a standard carbine buffer and spring, and then adjust the gas as needed.

firemn260 · Dec 20, 2019

andy41567 said:
very good guys. thanks.
i have an SLR adjustable gas block. Guess i will throw that on their instead of the fixed SLR i got for it.

I’m putting together a 300blk pistol myself. I have used the slr sentry 7 on all the rifles I have put together and I like the ability to tune the gun in, not having to worry so much about buffer weights and such. I know it’s not the end all be all solution to a well running weapon but it has worked for me. I put one on the 308 I assembled with the plan of running it suppressed one day. Ar308/ar10 are notorious for being over gassed as it is so I was able to dial it back to a ***** cat to shoot.

I’m not to familiar with the 300 blk cartridge so I’m looking forward to tinkering with it. I had a pretty low budget on this one so I stuck with mostly psa components which limited me to a 1/8 twist barrel. We shall see. Good luck with your pistol.

Ar pistol build laws

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