The tee that you see will have a shrader valve on the bottom for filling and a port for two wires for the ignition. The method of firing the gun is to use compressed air behind the piston to seal it aginst the barrel. when the piston moves back it will slide the tube back exposing holes in it to let out the air to allow the full power of the shot to go out the barrel.
there is still a lot of work to do to get it ready to fire. Here is the pictures.












