it doesnt have to work, only potential to work when assembled, otherwise the whole federal definition of receiver, and firearm starts to crumble into something

it doesnt have to work, only potential to work when assembled, otherwise the whole federal definition of receiver, and firearm starts to crumble into something approaching reality. for example a 2x4 profiled to fit an AR upper, and having one [!] hole [!] drilled where the trigger group belongs, is considered a firearm; if you dont drill in to the FCG pocket you have a lower blank [not a firearm yet]