300BlkTalk

I have a tax stamped 300 blackout with a 9" barrel. (Thanks all for helping, you made it so much easier)

Anyways. I know I can put a 16" upper on it, no big deal. But, am I allowed to put a 14" upper on it, or can I go shorter than the 9", and put a 7.5" 223 upper on the lower, or do I have to get a stamp and build a new rifle with the barrel length specified on its own Form 1?

Thanks.

Technically the law is silent on this and this is by no means legal advise.

When you submitted your stamp, you specified caliber and barrel length.

You also specified a serial number.


The NFA registry can only assign one serial number to one owner/trust/... at a time.

But if you submit a form 20 for the serial number to cross state lines, and specify a different caliber/barrel length, they will reject it saying it’s not a known configuration.

So it’s legal gray area. But you have a stamp for a registered lower. Imnsho that is plenty of due diligence on your part. If it helps, I routinely put different uppers on my registered lower(s).

I do the same thing. I suspect when the suppressor law was written, the erector set way of firearm construction was limited, i.e. no AR types.

Going from memory, as long as it can be configured (or reconfigured) into it's description on the form, you can put what ever upper you want on it. They grey area comes in when you have multiple SBR uppers, only one registered lower and a spare non-registered lower sitting in the safe. Many people configure the unregistered lower with a pistol brace. I just keep collecting stamps and sleep good at night.

Good luck.