Abstract: A piston and cylinder assembly for a gas powered gun, has a cylinder containing a piston rod slidably movable between a loading position in which the leading end of the piston rod is in a withdrawn position, and a firing position in which the piston rod has moved forwardly. The cylinder has first and second chambers through which the piston rod extends, the cylinder being connectable to a pressurized gas supply supplying pressurized gas to the first chamber when the piston rod is in the loading position. The piston rod permits communication between the pressurized gas supply and the first chamber and prevents communication between the first and second chambers when in the loading position, and when in the firing position prevents communication between the pressurized gas supply and the first chamber and permits communication between the first chamber and the second chamber to cause pressurized gas in the first chamber to pass into the second chamber.