ok, so it was never actually a machine gun, but due to the ambiguous rules and regulations governed by backwards nomenclature and nonsensical bureaucratic jargon its illegal because the ATF thinks its a machine gunIt has nothing to do with a full auto sear. The receiver having the third "hole" (for the full auto parts) makes the receiver a machine gun in the eyes of the ATF. These that were imported had semi-auto trigger parts and fired in semi-auto only. But because the receiver was a "machine gun" receiver, it's a machine gun.
Even with a pin or rivit in the 3rd hole it's still a machine gun. If you weld the 3rd hole shut it's still a machine gun.
so its a machine gun because they say so?