Cal. Penal Code § 17015

“Pistol converter” means any device or instrument that when installed in or attached to the rear of the slide of a semiautomatic pistol, replaces the backplate, and interferes with the trigger mechanism and thereby enables the pistol to shoot automatically more than one shot by a single function of the trigger. A pistol converter includes, but is not limited to, a pistol converter manufactured using a three-dimensional printer, as defined in Section 29185.