A rotary ammunition magazine cooperates with a bolt catch to hold the bolt of a firearm out of battery in an open position after the last round has been fired. A cam mounted on the rotor of the magazine actuates a movable body on the magazine housing as the cam rotates to feed ammunition to the action. The body moves to an extended position and engages a bolt catch pivotably mounted in the firearm receiver. The bolt catch is pivoted by the body into a position where it will engage the bolt and prevent it from returning to battery after the last round has been fired.