In CA...
IT WILL NOT BE LEGAL on a semi-auto centerfire rifle or semi-auto pistol.
The bullet button magazine lock makes the rifle/pistol a fixed magazine rifle/pistol.
A semi-auto centerfire rifle with a fixed magazine capacity greater than 10 rounds is an assault weapon. [PC 12276.1(a)(2)]
A semi-auto pistol with a fixed magazine capacity greater than 10 rounds is an assault weapon. [PC 12276.1(a)(5)]
Using a large capacity magazine in a semi-auto centerfire rifle/semi-auto pistol with a bullet button/magazine lock, will create an unregistered assault weapon (CA Felony). [PC 12280(a)(1)]
It is legal to use large capacity magazines in a semi-auto centerfire rifle that is "featureless", meaning it does not have any features that would define it as an assault weapon [PC 12276.1(a)(1)].
In CA...
Use only 10 round or less magazines in semi-auto centerfire rifles/semi-auto pistols that are equiped with a bullet button/magazine lock.
Penal Code 12276.1
(a) Notwithstanding Section 12276, "assault weapon" shall also mean any of the following:
(1) A semiautomatic, centerfire rifle that has the capacity to accept a detachable magazine and any one of the following:
(A) A pistol grip that protrudes conspicuously beneath the action of the weapon.
(B) A thumbhole stock.
(C) A folding or telescoping stock.
(D) A grenade launcher or flare launcher.
(E) A flash suppressor.
(F) A forward pistol grip.
(2) A semiautomatic, centerfire rifle that has a fixed magazine with the capacity to accept more than 10 rounds.
(3) A semiautomatic, centerfire rifle that has an overall length of less than 30 inches.
(4) A semiautomatic pistol that has the capacity to accept a detachable magazine and any one of the following:
(A) A threaded barrel, capable of accepting a flash suppressor, forward handgrip, or silencer.
(B) A second handgrip.
(C) A shroud that is attached to, or partially or completely encircles, the barrel that allows the bearer to fire the weapon without burning his or her hand, except a slide that encloses the barrel.
(D) The capacity to accept a detachable magazine at some location outside of the pistol grip.
(5) A semiautomatic pistol with a fixed magazine that has the capacity to accept more than 10 rounds.
(6) A semiautomatic shotgun that has both of the following:
(A) A folding or telescoping stock.
(B) A pistol grip that protrudes conspicuously beneath the action of the weapon, thumbhole stock, or vertical handgrip.
(7) A semiautomatic shotgun that has the ability to accept a detachable magazine.
(8) Any shotgun with a revolving cylinder.