A firearm is defined as any weapon (including a starter gun) that will expel a projectile by means of an explosive—or is designed or may be readily converted to do so. This includes the frame or receiver of any such weapon, any firearm muffler or silencer, or any destructive device.

A destructive device includes any explosive, incendiary, or poison gas—(i) bomb; (ii) grenade; (iii) similar device; or (iv) any combination of parts designed or intended to be converted into a destructive device, or from which a destructive device may be readily assembled. A destructive device does not include black powder or antique type firearms. 18 U.S.C. §921(3).

It is a federal criminal offense—punishable by up to 5-10 years imprisonment, depending on the specific violation—to knowingly possess or manufacture:

• Any machine gun, fully automatic firearm, or any part designed or intended exclusively for use in such weapon;

• A firearm silencer, including any device, or part thereof, designed to silence, muffle or diminish the report of a firearm;

• A sawed-off shotgun with a barrel length of less than 18" or overall length less than 26";

• A sawed-off rifle with a barrel length of less than 16" or overall length less than 26";

• A destructive device;

• A semi-automatic assault weapon manufactured after October 1, 1993; or

• A firearm that lacks a serial number or contains an altered or obliterated serial number.

18 U.S.C. § 922(k), (o) & (v); 26 U.S.C. § 5861.

And federal firearms laws prohibit transactions in and possession of certain types of firearms. These include, for example:

• Transfer or possession of a machinegun—18 U.S.C. §922(o);

• Manufacture, importation, sale, or possession of any firearm not detectable by airport security devices—18 U.S.C. §922(p); and

• Possession of a firearm not registered as required by the National Firearms Act (NFA)—26 U.S.C. §5861(d).

In California, a firearm is broadly defined to include any weapon that can expel a projectile by means of an explosive, or that can be readily converted to do so. This definition encompasses the frame or receiver of the weapon, as well as firearm mufflers, silencers, and destructive devices such as bombs, grenades, and other similar items, with certain exceptions for antique firearms. Under federal law, specifically 18 U.S.C. § 921(3) and related statutes, it is a criminal offense to knowingly possess or manufacture certain types of firearms and devices, including machine guns, fully automatic firearms, firearm silencers, sawed-off shotguns and rifles, destructive devices, semi-automatic assault weapons manufactured after October 1, 1993, and firearms with missing or altered serial numbers. Penalties for these offenses can range from 5 to 10 years imprisonment. Additionally, federal law prohibits the transfer or possession of machine guns, the manufacture or possession of undetectable firearms, and the possession of unregistered firearms as required by the National Firearms Act (NFA). These regulations are enforced to control the possession and distribution of potentially dangerous firearms and devices, and to ensure public safety.