Cal. Penal Code § 16880

(a) As used in this part, “machinegun” means any weapon that shoots, is designed to shoot, or can readily be restored to shoot, automatically more than one shot, without manual reloading, by a single function of the trigger. (b) The term “machinegun” also includes the frame or receiver of any weapon described in subdivision (a), any part designed and intended solely and exclusively, or combination of parts designed and intended, for use in converting a weapon into a machinegun, and any combination of parts from which a machinegun can be assembled if those parts are in the possession or under the control of a person. (c) The term “machinegun” also includes any weapon deemed by the federal Bureau of Alcohol, Tobacco, Firearms and Explosives as readily convertible to a machinegun under Chapter 53 (commencing with Section 5801) of Title 26 of the United States Code. (d) The term “machinegun” also includes any machinegun-convertible pistol equipped with a pistol converter, as defined in Section 17015.