@arh@toots.alirezahayati.com looks like i'm not the only one with this idea lol:
https://palmettostatearmory.com/guns/ak-rifles-pistols/ak-rifles.html
@icedquinn @arh@toots.alirezahayati.com the lower receiver has always been "legally a gun". buying a lower receiver, even if not fitted out with trigger, upper, whatever, is still "buying a firearm" for legal purposes.
you have to buy a lower that isn't completed, which is uncontrolled, and do a bit of aluminum milling yourself, then add the upper and trigger parts (also all uncontrolled). it's still common and legal to do so.
in states like Texas, rifles assembled by the owner do not need to be registered either.