 During this rearward movement, a cam slot machined into the bolt carrier engages a cam pin on the bolt and rotates the bolt, unlocking the action.The arrangement of parts on the bolt carrier assembly provides for a degree of free travel, allowing gas pressure in the barrel to drop to a safe level before unlocking.To the immediate rear of the chrome-plated piston head is a notched ring which provides a reduced bearing surface and alleviates excess gas build-up.