The grip is what makes it CA legal....its called a monster grip,its what allows the owner to have a detachable mag, (don't need a bullet button) I "have" one on my new Rock River Tactical Entry AR...still can't have hi-cap mags tho...

ha.
It basically doesn't allow the shooter to have apt control over the weapon, forcing the shooter to hold it like a rifle, and the ergonomics suck ass. With a pistol grip it is so much better.