California law states you cannot have a detachable mag over 10 rounds, so the mag release on an AR15 is a bolt, not a push button.
That is incorrect and almost backwards. It is over 10 rounds period that is not allowed, except detachable grandfathered magazines.
The issue is also two seperate laws, one is a magazine ban on magazines not possessed prior to the year 2000, while the other is part of the definition of assault weapon and applies only to fixed magazine firearms, not those with detachable magazines.
Fixed magazines over 10 rounds (other than tubular rimfire and some exemptions) are always an assault weapon, while grandfathered detachable magazines possessed prior to 2000 in CA are legal.
The result is if you were to for example put a legal grandfathered detachable 30 round magazine into a firearm that has a bullet button you would be creating an illegal assault weapon. Even though possession and use of the magazine is legal, creating a gun with a fixed magazine over 10 rounds is a felony punishable by 10 years in prison.
While putting the same magazine in a gun without a bullet button that is otherwise legal is okay because that gun is not compliant via bullet button but via other features. Like an SU-16 or mini 14, m1a, or AR/AK with special non-pistol grip stock modification and no other features.
This is because the state Assault Weapon definition includes all fixed magazine guns over 10 rounds, and since the whole way bullet buttons make guns otherwise restricted legal is by turning them into fixed magazine firearms not subject to the feature restrictions of detachable magazine firearms, inserting a magazine over 10 rounds is creation of a firearm with a fixed magazine over 10 rounds. All by itself the definition of an unlawful assault weapon with no other feature.
While the assault weapon definition does not include guns with over 10 round detachable magazines. So inserting a magazine over 10 rounds into a gun that accepts detachable magazines (no tool needed to remove) is legal, and only the magazines are not legal.
While illegal possession of a magazine greater than 10 rounds is a lesser crime, and harder to prove.
So ironically inserting a magazine over 10 rounds into a bullet buttoned firearm is actually a much more serious crime than illegal possession and use of a magazine over 30 rounds in an otherwise legal firearm without a bullet button.
So use of a bullet button actually ups the stakes.
Many people are unaware of this. I see people at ranges use magazines over 10 rounds in bullet button firearms. Convinced the issue is whether the magazine is legal or not.
They have no idea they are committing multiple felonies as they swap magazines with thier legally possessed (or illegally possessed that they presume cannot be proven to be from after 2000) magazines.
On the bright side they probably won't actually get 10 years, just become felons, lose thier firearms, and get probation or be out on parole in no time to make room for criminals they consider more important to actually keep locked up.