From Guns.com:

“California law presently permits the lethality of a gun with a 10-round magazine. In other words, a gun with an 11-round magazine or a 15-round magazine is apparently too lethal to be possessed by a law-abiding citizen. A gun with a 10-round magazine is not,” he said, arguing that, following the same logic, the state could further move to drop the capacity, “until the time comes when government declares that only guns holding a single round are sufficiently lacking in lethality that they are both ‘safe’ to possess and powerful enough to provide a means of self-defense.”