Abstract: In a taphole gun for use in closing tapholes in blast furnaces and the like, a tamping piston is axially displaceable through a cylinder for forcing tamping material into the taphole. An annular recess is formed in the circumferential periphery of the tamping piston and a piston ring is fitted into the annular recess. The piston ring is dimensioned relative to the recess so that tamping material enters the recess and exerts pressure on the piston ring forcing it radially outwardly against the inner surface of the cylinder and axially against the tamping piston.