The types of firearms that must be registered in the National Firearm Registration and Transfer Record are defined in the NFA and in 27 CFR Part 479. What are some examples?
Some examples of the types of fire- arms that must be registered are:
Machine-guns;
The frames or receivers of machine-guns;
Any combination of parts designed and intended for use in converting weapons into machineguns;
Any part designed and intended solely and exclusively for converting a weapon into a machinegun;
Any combination of parts from which a machinegun can be as- sembled if the parts are in the pos- session or under the control of a person;
Silencers and any part designed and intended for fabricating a silencer;
Short-barreled rifles; Short-barreled shotguns; Destructive devices; and, "Any other weapon."
A few examples of destructive devices are:
Molotov cocktails; Anti-tank guns (over caliber .50); Bazookas; and, Mortars.
A few examples of "any other weapon" are:
H&R Handyguns; Ithaca Auto-Burglar guns; Cane guns; and, Gadget-type firearms and "pen" guns which fire a projectile by the action of an explosive.
[26 U.S.C. 5845] - FEDERAL FIREARMS REGULATIONS REFERENCE GUIDE 2015