The judge's ruling does not make "common use" a requirement, its the opposite. He is rejecting common use as a "means test" because that is the justification California tried to use to impose the ban.
California posed the "commonly used" angle by citing a statistician that said 2.2 rounds was the most common number of bullets fired in a self defense scenario:
Because more than 10 rounds in the average situation are not being fired for self-defense, the argument goes, magazines holding more than 10 rounds are not used or needed for self-defense. And because the Second Amendment protects (according to the State) only those arms commonly “used” for self-defense, the State says larger capacity magazines are not commonly “used,” and therefore they are not protected arms
He then rejects it by first noting that "used" really means "fired", and then:
The Supreme Court has not said that the actual firing of a gun is any part of the test. Indeed, the Second Amendment does not say that the right of the People to keep only such firearms as they actually shoot, shall not be infringed.
Thank you for the correction.
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