A number of embodiments of a firearm are disclosed where the firearm includes a magazine configured to hold the bolt in an open position when the magazine is empty. In one embodiment, the firearm includes a bolt stop mechanism that moves between a first position where it allows the bolt to cycle between an open position and a closed position and a second position where it holds the bolt in the open position. The magazine is configured to actuate the bolt stop mechanism to the first position when the magazine is empty.