California Code, Penal Code - PEN § 17360

(a) It was not imported as a firearm by an importer licensed pursuant to Chapter 44 (commencing with Section 921) of Title 18 of the United States Code and the regulations issued pursuant thereto.

(b) It was not originally designed to be a firearm by a manufacturer licensed pursuant to Chapter 44 (commencing with Section 921) of Title 18 of the United States Code and the regulations issued pursuant thereto.

(c) No tax was paid on the weapon or device nor was an exemption from paying tax on that weapon or device granted under Section 4181 and Subchapters F (commencing with Section 4216) and G (commencing with Section 4221) of Chapter 32 of Title 26 of the United States Code, as amended, and the regulations issued pursuant thereto.

(d) It is made or altered to expel a projectile by the force of an explosion or other form of combustion.