Is it possible to build a SBR on a self finished 80% project lower? Obviously it would have to be registered and tax stamp etc, but there would be no serial #? Any thoughts on this? And can a SBR ever be converted back into a 16" rifle? Say if you moved from a state that does allow SBR to one that doesn't? Or must you sell the SBR? Just curious to see if it's worth it. Thanks for input.

You'd be required to put a serial number on an NFA lower, even if you built it from an 80%.  Re-using the original serial number of an existing lower is just a time-saving/convenience step.

If you later wish to remove the SBR from the NFA registry, you can do so by removing the short upper, and sending a letter to the NFA notifying them of the permanent alteration to non-NFA length, and requesting that the item be removed.

Keep in mind that an 80% receiver can only be legally configured in a post-ban configuration, so your SBR will be unable to have a collapsible stock, a flash suppressor, or a bayonet lug.

[:(]

Circuits, I am guessing that you would just make up a serial number? I guess it just seems a little different as "you" are the manufactuer and you would have to make up a serial #.

Treetop, thanks for the reminder. Some people may not realize this. I don't necessarily need all those features on this project. Plus it is a lot cheaper this way over a pre-ban, and I get the satisfaction of building it. Be nice if they realized how little difference it makes to crime and public safety weather or not an AR has a bayo lug or flash hider.

so what if you made this homemade reciever in 1989, and had a serial # and 1989 date stamped into the reciever. Could you build an sbr with pre-ban features?

Yes.  If the lower is pre-ban, you can build it into an SBR with pre-ban features once your NFA tax stamp on the Form 1 gets back to you from the ATF.

if u truly made it pre 94 and it had enought parts on it to be considered a "assualt weapon" yes u could