Form 1 Block 4 Questions

[26 Inf]

I have a stamp for my SBR, so my form 1 passed initial muster.

My question is this: Would I be illegal if I put a 12" 300 Blackout upper on a receiver that had 5.56 and 10 inches listed in Block 4?

I need to see something substantive beyond opinions, but have been unable to find anything.

Help anyone?

[MisterHelix]

It is my understanding that you can put whatever upper you want on it, as long as you can return it to the listed configuration.

*not a lawyer

[BigWaylon]

There's no requirement to be able to return it to the specs on the form.

The specs you provided are for the initial making of a firearm. That's a one-time act, with a specific caliber and length. Once that's done, you can configure it as you wish.

[Iraqgunz]

And you won't. It is still an SBR when you change it.

I have a stamp for my SBR, so my form 1 passed initial muster.

My question is this: Would I be illegal if I put a 12" 300 Blackout upper on a receiver that had 5.56 and 10 inches listed in Block 4?

I need to see something substantive beyond opinions, but have been unable to find anything.

Help anyone?