Even in light of my post in this thread, I am no where near a pro with this topic.. But I am confused, and you look like the FReeper I can turn to for an answer.
At the federal level, if you do completely fabricate an AR9 low end, you have to number it to be used in a pistol ?
What about things like 1911 blanks? These don’t require numbers, but an AR9 lower built for pistol does ? I’m confused.
If you purchase a stripped lower, it can be used for a rifle or a pistol build. A 1911 lower frame carries the serial number, and it, too needs to be transferred through an FFL. Whichever part of the firearm that has a serial number is the portion that needs the FFL transfer. A Ruger semi auto .22 pistol, for instance has the serial number on the upper half, So the upper half of that firearm is the portion that needs the FFL transfer.