Quite simply, possession of an M-1 carbine and a handfull of M-2 parts is considered "constructive" possession of an unregistered machine gun. Same goes for AR15 and M16 fire control parts. This includes lightening links and disconnectors such as still being sold by Suppress-On even if they're in your pocket! A guy without a Carbine or an AR can own as many as he wants, just don't bring 'em together. Kinda like 151 Rum and fire!