With certain exceptions a firearm may be made by a non-licensee provided it is not for sale and the maker is not prohibited from possessing firearms. However, a person is prohibited from assembling a non-sporting semi-automatic rifle or non-sporting shotgun from imported parts. In addition, the making of an NFA firearm requires a tax payment and approval by ATF. An application to make a machine gun will not be approved unless documentation is submitted showing that the firearm is being made for a Federal or State agency.
[18 U.S.C. 922(o) and (r), 26 U.S.C. 5822, 27 CFR 478.39, 479.62 and 479.105]