The NFA covers six kinds of firearms. Four now carry a $0 tax and lighter federal rules. Two still carry the full process.
Suppressors
Any device for silencing, muffling or reducing the report of a firearm, including parts meant only for building one. Suppressors are the most popular NFA item by far.
Short-barreled rifles and shotguns
A rifle with a barrel under 16 inches or a shotgun with a barrel under 18 inches, or either one under 26 inches overall.
Any other weapons (AOW)
A catch-all for concealable firearms that are not ordinary pistols or rifles: pen guns, cane guns, smooth-bore pistols and handguns with a vertical foregrip are common examples. AOWs exist because Congress dropped handguns from the 1934 bill but still wanted to cover guns that could be disguised.
Machine guns
Any weapon that fires more than one shot with a single function of the trigger, plus the parts that convert a gun to fire that way. Only guns registered before May 19, 1986 can go to private owners.
Destructive devices
Explosive devices like grenades and rockets, and most weapons with a bore over one-half inch, other than shotguns found suitable for sporting use.
