(b)(1) No person prohibited from owning or possessing a firearm under Section 12021 or 12021.1 of this code or Section 8100 or 8103 of the Welfare and Institutions Code shall own, possess, or have under his or her custody or control, any ammunition or reloaded ammunition.
(2) For purposes of this subdivision, "ammunition" shall include, but not be limited to, any bullet, cartridge, magazine, clip, speed loader, autoloader, or projectile capable of being fired from a firearm with a deadly consequence.

So a prohibited person cannot own a magazine.