Abstract: A firearm breech locking mechanism which includes a receiver having a longitudinal track guiding an actuating rod in reciprocating motion, and two guide slots for guiding a bolt carrier member mechanically coupled to the operating rod. Two roller receiving slots are also formed in the receiver member. A roller is disposed in these slots. It extends transversely to the direction of motion of the operating rod. A cam surface on the operating rod raises the roller as the operating rod reaches its forwardmost position to thereby lock the bolt relative to the receiver and shell chamber. As the operating rod is moved rearward, a cam surface on the bolt carrier forces the roller to its unlocked position. The invention further includes a latch pivotally secured to the bolt member which cooperates with a recess formed along one of the guide slots.