Patent ID: 7934493

Claim:
A self-loading bolt assembly ( 6 , 9 , 10 ) for an air gun comprising: a cylinder ( 10 ) formed coaxially in a breech portion of a barrel ( 2 ); a hollow piston ( 6 ) coaxially loosely-fitted in the cylinder ( 10 ) so as to be movable relative to the cylinder ( 10 ); and, a firing pin ( 9 ) coaxially incorporated into the hollow piston ( 6 ) so as to be movable relative to the hollow piston ( 6 ); wherein the cylinder ( 10 ) assumes a tubular shape constructed of a front small-diameter portion and a rear large-diameter portion, the hollow piston ( 6 ) is loosely-fitted in the cylinder ( 10 ) so as to be axially movable relative to the cylinder ( 10 ), a clearance ( 11 ) between the cylinder ( 10 ) and the hollow piston ( 6 ) is enlarged when the hollow piston ( 6 ) has its rear portion entered the rear large-diameter portion of the cylinder ( 10 ) to permit a compressed gas to readily enter a compressed-gas receiving portion ( 5 ) of the rear portion of the hollow piston ( 6 ) through the clearance ( 11 ) thus enlarged so that hollow piston ( 6 ) is driven forward toward a muzzle of the barrel ( 2 ) thereby forcing a bullet ( 1 ) to be positioned in a predetermined firing position in a powder chamber of the barrel ( 2 ), wherein the firing pin ( 9 ) assumes a rod-like form and receives the pressure of the compressed gas at its rear large-diameter shoulder portion ( 12 ) to move rearward in the reverse direction opposite to the direction toward the muzzle of the barrel ( 2 ) thereby forcing an opening portion of a third O-ring (O 3 ) clogged with the firing pin ( 9 ) to open so as to spout a jet of the compressed gas toward a rear surface of the bullet ( 1 ) to propel the bullet ( 1 ) forward, wherein air confined between a front wall of the cylinder ( 10 ) and the hollow piston ( 6 ) loosely-fitted in the cylinder ( 10 ) is compressed when the hollow piston ( 6 ) moves forward relative to the cylinder ( 10 ) so that the air thus compressed escapes through the clearance ( 11 ) between the hollow piston ( 6 ) and the cylinder ( 10 ) toward the rear of the hollow piston ( 6 ), thereby preventing the air thus compressed from disturbing forward motion of the hollow piston ( 6 ) relative to the cylinder ( 10 ).