Abstract: In a high-energy rate forging machine the piston, to which a ram is attached, is driven towards a workpiece by a high pressure gas supplied to the space above the piston within a cylinder. The space above the cylinder and the space below the cylinder are joined by holes in the cylinder and grooves in the cylinder walls. The grooves are only effective when the piston is at about the middle to lower part of its stroke. They are blocked when the piston is at or near the top part of its stroke. High speed stamping is provided without double or triple stamping and with a smooth return stroke of the piston.