Cal. Fish & Game Code § 2010

It is unlawful to use or possess a shotgun larger than 10-gauge, or to use or possess a shotgun capable of holding more than six cartridges at one time to take any mammal or bird. However, the commission may, after public hearing, adopt regulations relative to the ammunition capacity of shotguns for taking mammals or birds that are further restrictive or that it determines may be needed to conform to federal law. Shotguns that have been modified with the insertion of a plug are deemed, for the purpose of this section, to have a cartridge capacity equal to the number of cartridges that can be loaded into the weapon as modified.