SIG P556 Pistol 10" to SBR - Proper NFA Forms? (New Hampshire)

[MaverickNH]

I have a SIG P556 Pistol with 10 inch barrel. Built on the AK design, the upper is the sterilized part, not the lower. I’d like to mate that with a SIG 556 folding stock lower to make a SBR. The two parts have never met and live in different places, but others have mated them with no problems, so I figure it’ll work.

Which Form(s) do I need to file with ATF? I’m a NH resident, so no state issues.

 

[42!]

ATF eForm 1 mega thread. Process and approvals!

 

[ScottS]

It can, and should, be done electronically. eForm 1.