[aziator]

Well, A Bullet Button Mag lock is a lock that requires a tool to release the magazine.

http://www.tenpercentfirearms.com/index.php?main_page=product_info&products_id=265

http://www.riflegear.com/c-15-california-legal.aspx

Looks like model 1 and 3 both come with the crazy mag lock.