Abstract: An air-powered gun adapted to be loaded with a plastic material such as a caulking compound from a bulk container thereof, and to dispense the same through a nozzle wherein the gun is comprised of a forward loading and dispensing barrel and an oppositely extending coaxial piston-driving rear air barrel, both of which barrels are held in back-to-back receptacles in a body gripping member provided with a handle. A piston slidable in the forward barrel is connected by a shaft to a piston in the rear barrel, which shaft extends coaxially through an orifice in the body gripping member passing through the bottom of both receptacles. Two plunger valves are provided in the handle, one to direct air into the receptacle for the forward barrel, and the other, to that for the rear barrel. A removable nozzled dispensing cap is provided for the outer end of the forward barrel.