A firearm-magazine interface for replacing an existing firearm-magazine interface of many existing firearms such as assault rifles, namely AK series (AK74, AK47, etc.) provides a lock that holds open the bolt after a last round is fired from a magazine. The firearm-magazine interface also includes a single-button magazine eject. After firing the last round, a bolt-hold lock is urged upwardly in the path of the returning bolt and catches a face of the bolt, thereby locking the bolt open until the magazine is replaced with a replacement magazine, at which time a bolt-hold release paddle pulls the bolt-hold lock downwardly, releasing the bolt to chamber a first round from the replacement magazine.