View Full Version : SBR technical question

November 5, 2009, 01:57 PM
I tried to search for this specifically but found answers all around the question but not directly answering it.

So I want to create an AR SBR. Can a AR Pistol lower be converted with a new buffer tube and stock? Or is there a technical difference that prevents this.

Of course I am going to do this legally so forget those comments please. Im just trying to find the most effective means.

November 5, 2009, 02:01 PM
No difference. An AR pistol receiver is the same receiver used on a rifle (most of the time, there are a few oddballs out there, very uncommon).
By adding a shoulder stock to a pistol you are creating a SBR. Just like if you put one of those stock things on a Glock, adding the rec ext and stock to the AR pistol you have now made a rifle.


November 5, 2009, 03:46 PM
Best way is to set up your pistol how you want your SBR, make sure it works for you and runs. If it's good to go, file your form one, and when approved, slap on a stock.

November 5, 2009, 05:20 PM
Sweet that was my plan but I wanted to make sure of compatibility. Ive never held a pistol AR and had heard that they were dedicated pistol lowers. I just wasnt sure.

Thanks for the info. Now I need to figure out which one to buy. The fun part!

November 5, 2009, 05:41 PM
If I'm reading this right:

You have a .223/5.56 Pistol.

1. You would like to register it as a SBR and put a stock on it.

2. You would like to get a second upper and put a SBR 9mm Carbine together too.

If my guess is RIGHT, You WILL need a new tube with a stock +/- spring. Additionally, you *may* need a second buffer +/- buffer spring for the 9mm. You may need a "hookless" hammer for the 9mm as well.

The AR pistol length gas systems put a lot of pressure into the gas tube and therefore push on the bolt carrier group rather violently. They use a pretty heavy buffer to combat the elevated pressures from the short gas tube.

The AR 9mm uppers are blow back. They may work with the heavy buffer and spring, but may not. Be sure that your hammer is correct for the bolt on the 9mm upper. If they are RAMPED BOLT CARRIERS, then you can still use the "traditional" AR hammer. If it is NOT ramped, then you need the 9mm hammer without the "hook" on it. The hook will cause "early cocking" of the hammer as well as put a lot of stress on the hammer pin at least. In the worst case, it can bind up between the bolt carrier and hammer, and that can be a BIG headache. (When the bolt is bound up partially open you can't remove the upper from the lower.)

EDIT: The need to intechage all these parts each time I want to switch calibers really pushed me towards a dedicated 9mm Carbine build. FWIW.

Sasquatch in MN
November 5, 2009, 05:51 PM
Though the DPMS hammers will work on the Colt/RRA type 9mm uppers, I'd recommend swapping a 9mm hammer in with the 9mm buffer when using the 9mm upper.

Also, don't forget to get your lower engraved before you get your approved form 4 back. Remember to register it on the F4 as both 9mm and 223 or you'll need to send a letter of intent to the NFA branch to update your NFA status.


November 6, 2009, 12:44 AM
Remember to register it on the F4 as both 9mm and 223 or you'll need to send a letter of intent to the NFA branch to update your NFA status.

sorry to hijack your thread but quick question...exactly how many calibers can you put on a form 4 for 1 SBR?

Sasquatch in MN
November 6, 2009, 01:45 AM
Multi calibers is OK from what I've heard. On my personal SBR's , they were F4 as .223 and I send a letter of intent to utilize different barrel lengths and calibers in a letter to the NFA branch requesting that they update the status of the NFA firearm in question. Once they acknowledge receipt of the letter, any config you advised them of is good to go.

November 6, 2009, 06:38 AM
I actually havent bought anything yet. I was just contemplating which way to go. I originally wanted a 9mmAR, but I would want to SBR it. Anyway I am still in research mode.

November 6, 2009, 08:39 AM
Remember to register it on the F4 as both 9mm and 223 or you'll need to send a letter of intent to the NFA branch to update your NFA status.

Multi calibers is OK from what I've heard.

You never know what is going to slip through different examiners at the NFA branch but “Multi” and a range of lengths are not ok anymore. You can list additional calibers in 4h of the form 1, you should just have the upper described on the f1 handy at all times.
You'll just waist time turning in something wrong so just give them a call at 304-616-4500 with your questions.