How can an individual legally acquire NFA firearms?
Basically, there are 2 ways that an individual (who is not prohibited by Federal, State, or local law from receiving or possessing firearms) may legally acquire NFA firearms:
(1) By transfer after approval by ATF of a registered weapon from its lawful owner residing in the same State as the transferee.
(2) By obtaining prior approval from ATF to make NFA firearms.
[27 CFR 479.62-66 and 479.84-86] - FEDERAL FIREARMS REGULATIONS REFERENCE GUIDE 2015