A valve assembly for supplying air under pressure to the firing chamber of an air gun includes a hollow cylindrical chamber which houses a slidable piston whose external diameter is slightly less than the internal diameter of the cylindrical chamber to define an airflow passage therebetween. Air under pressure is admitted to that portion of the chamber interior which lies to one side of the piston and the piston is moved along the chamber immediately before release of the air from the chamber in a sense further to compress the air present therein. The re-compressed air can then be selectively released from the cylindrical chamber to the firing chamber of the air gun. <IMAGE>
