Any cylinder able to hold the pressure will work but the hammer valve on the end of the cylinder is the item that is needed the most, Mikes own invention and no other valve in the world is going to fit. The hammer hits the valve that is in the bottle to put a shot of air through the rifle hence the rifle is never under pressure so the cylinder can be removed at any time safely, The problem being is that there is not much room for the valve to fit into the skans rifles cavity.. Imagine the gunpower stealth who used the same idea, Same principle of letting a shot of air out of the bottle when the hammer hits the bottle valve.. But its way to big for the skans, The r32 uses the standard bottle we know today but the original valve is also attached to the front of it. ie rapid bottle connected to skan valve then screw to rifle.. Col.