serial number placement question and transfer paperwork

[MNShooter]

Originally Posted by Ron Wood

It is the frame, and that isn't a guess. It seems odd, I know, since technically the "upper" (barrel, receiver and toggle train) is a firearm capable of firing a cartridge independent of the frame. But as far as the BATFE is concerned, the frame is the controlled part and requires a FFL for transfer.

Ron, Thank you.