The National Firearms Act of 1934 (NFA) requires the registration, with the federal government, of fully-automatic firearms (termed “machineguns”), rifles and shotguns that have an overall length under 26 inches, rifles with a barrel under 16 inches, shotguns with a barrel under 18 inches, and firearm sound suppressors (termed “silencers”). The Gun Control Act of 1968 (GCA) placed “destructive devices” (primarily explosives and the like, but also including firearms over .50 caliber, other than most shotguns) under the provisions of the NFA. In 1994, the Treasury Department placed revolving-cylinder shotguns and one semi-automatic shotgun under the NFA.
The GCA prohibited the importation of fully-automatic firearms for private purposes and a 1986 amendment to the Act prohibited the domestic manufacture of fully-automatics for private purposes. However, short-barreled rifles and shotguns have becoming increasingly popular for home defense and defensive-skills-based marksmanship training and competitions, and sound suppressors have become increasingly popular for marksmanship training and competitions, and for hunting.