California Code, Penal Code - PEN § 16520

(a) As used in this part, “firearm” means a device, designed to be used as a weapon, from which is expelled through a barrel, a projectile by the force of an explosion or other form of combustion.

(b) As used in the following provisions, “firearm” includes the frame or receiver of the weapon, including both a completed frame or receiver, or a firearm precursor part:

(c) As used in the following provisions, “firearm” also includes a rocket, rocket propelled projectile launcher, or similar device containing an explosive or incendiary material, whether or not the device is designed for emergency or distress signaling purposes:

(d) As used in the following provisions, “firearm” does not include an unloaded antique firearm:

(e) As used in Sections 34005 and 34010, “firearm” does not include a destructive device.

(f) As used in Sections 17280 and 24680, “firearm” has the same meaning as in Section 922 of Title 18 of the United States Code.

(g) As used in Sections 29180 to 29184, inclusive, “firearm” includes the completed frame or receiver of a weapon.