I agree with TMH
Not legal advice, but here’s the two CA Penal code sections that apply:
As used in Chapter 9 (commencing with Section 33410) of Division 10 of Title 4, “silencer” means any device or attachment of any kind designed, used, or intended for use in silencing, diminishing, or muffling the report of a firearm. The term “silencer” also includes any combination of parts, designed or redesigned, and intended for use in assembling a silencer or fabricating a silencer and any part intended only for use in assembly or fabrication of a silencer.
(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.