32 C.F.R. § 552.100 – Definitions.

(a) Ammunition. Projectiles together with their fuses, propelling charges, and primers that are designed to be expelled from a firearm. This includes any type of military and commercial ammunition (ball, tracer, incendiary, blank, shotgun, black powder, and shot). Items shall only be considered as ammunition when loaded into a cartridge with its bullets and primer.
(b) BB and pellet guns. Any type rifle, pistol or other instrument designed or redesigned, made or remade, modified or remodified to expel BBs or pellets by springs, compressed air, CO2 or any other compressed gas cartridge.
(c) Dangerous instruments. Any device which is designed or redesigned, made or remade, modified or remodified to be used as an offensive or defensive weapon. Devices of this type include but are not limited to:
1. (1) “Constant companion” or any similar weapon, designed or redesigned, made or remade, modified or remodified to be worn as a belt buckle, brass kunckles, “Knucklers,” and “Knucks.”
2. (2) Studded or spiked wrist bands, or any device designed or redesigned, made or remade, modified or remodified to fit over the hand or wrist which can be used to cause grave bodily harm.
3. (3) Black jacks, slapjacks, slappers, saps, including homemade substitutes, other bludgeons (with or without handles), and metal pipes.
4. (4) “Nanchaku” (num-chucks), two or more sticks connected by rope, cord or chain and normally used as a martial arts weapon. “Shuriken”, a disc or any geometrical object designed to be thrown as a weapon. “Manrikigusari” or “Kusari,” a rope or cord joined to a weight at each end and designed to be used as a weapon.
5. (5) Any finger ring with blades or sharp objects that are capable of being projected/extended from the surface of the ring.
6. (6) Any device capable and primarily intended for discharging darts or needles.
7. (7) All firearms.
(d) Explosive, incendiary, and pyrotechnic devices. Any type of military or commercial explosive, incendiary, gas or smoke bomb, grenade, rocket, missile, mine, blasting cap, “dummy” and/or practice device such as simulators, and other similar detonating devices which are capable of being altered to contain a live charge, and pyrotechnic devices such as firecrackers, cherry bombs, bottlerockets, and starclusters.
(e) Firearms. Any type of weapon which is designed or redesigned, made or remade, modified or remodified to expel a projectile by action of any explosion, and the frame or receiver of any such weapon. This does not include antique firearms, antique replicas, and those modern firearms which have been rendered permanently incapable of being fired.
(f) Knives, sabers, swords, and machetes. Any instrument having a sharp blade which is fastened to a handle, or made with a handle. Measurement of the blade will be from the tip of the blade to the point where the blade meets the handle. This includes folding knives, switchblades, gravity knives, stilettos, lock blade knives, swords, sabers, and machetes.
(g) Machine gun and automatic weapon. A weapon designed or redesigned, made or remade, modified or remodified to automatically fire more than one shot by a single pull of the trigger.
(h) Public gathering. Shall include, but shall not be limited to, athletic or sporting events, schools or school functions, churches or church functions, rallies, or establishments at which alcoholic beverages are sold for consumption on the premises.
(i) Shotgun. A weapon designed or redesigned, made or remade, and intended to be fired from the shoulder; and designed or redesigned, made or remade, to use the energy or the explosive in a fixed shotgun shell to fire through a smooth bore either a number of ball shot or a single projectile for each single pull of the trigger.
(j) Sawed-off shotgun. A shotgun or any weapon made from a shotgun whether by alteration, modification, or otherwise having one or more barrels less than 18 inches in length or if such weapon as modified has an overall length of less than 20 inches.
(k) Sawed-off rifle. A weapon designed or redesigned, made or remade, and intended to be fired from the shoulder; and designed or redesigned, made or remade, to use the energy of the explosive in a fixed metallic cartridge to fire only as a single projectile through a rifle bore for each single pull of the trigger; and which has a barrel or barrels of less than 16 inches or has an overall length of less than 26 inches.
(l) Silencer. Any device used for suppressing or diminishing the report of any firearm.
(m) Weapon. An instrument used in an offensive or defensive manner.