Abstract: A semi-infinitely-adjustable butt stock assembly. A butt stock is slidably affixed to a buffer stem. An over-center lock is attached to the butt stock adjacent to the buffer stem. The user can disengage the over-center lock from the buffer stem by rotating a lever thereby permitting the longitudinal position of the butt stock to be adjusted relative to the buffer plate. To secure the butt stock at the desired position, the user rotates the lever in the opposite direction causing the over-center lock to re-engage the buffer stem. A cheek rest overlaying the butt stock and biased forward with respect thereto is adjustable vertically with respect to the butt stock by manually moving the cheek rest aft, adjusting it vertically, and releasing the cheek rest.