A projectile launching apparatus for cleaning the inner surface of a tube by forcing a projectile through the tube, comprising: a main body containing a breech chamber terminating in an exit port, wherein the breech chamber is provided with a loading port in a side thereof for radially loading a projectile into the breech chamber; a slide disposed on an exterior surface of the main body, the slide being axially movable between a first position wherein the loading port is exposed for loading of a projectile into the breech chamber and a second position wherein the loading port and the breech chamber are sealed; a gas gun operatively connected to the main body in pneumatic communication with the breech chamber; and an exit nozzle connected to the exit port and being connectable to a first end of the tube to be cleaned.