Like barrels and triggers, magazines are essential for the operation of all multi-shot and repeating firearms, which are "bearable arms." The word "arms" must extend to these essential components of firearms. If it did not, the government could ban all magazines and limit individuals to single-shot firearms. Before Bruen the circuit courts consistently treated magazines as arms, including Ass'n of New Jersey Rifle & Pistol Clubs, Inc. v. Att'y Gen. New Jersey (3d Cir. 2018), New York State Rifle & Pistol Ass'n , Inc. v. Cuomo (2d Cir. 2015), and Heller v. District of Columbia (D.C. Cir. 2011).
Since magazines holding over ten rounds are "arms," it is California's burden to prove that they are "not typically possessed by law-abiding citizens for lawful purposes," which it cannot do.
In sum, when the Second Amendment's "plain text" covers conduct, it is presumptively protected. It is then the government's burden to show that a restriction is consistent with this Nation's historical tradition of firearm regulation.