The launching of an unmanned projectile includes pre-packaging a barrel with a projectile, a pusher cup, and a gas generator. The gas generator generates gas to propel the projectile out of the barrel. A pressure chamber increases a pressure of the gas in the barrel. The pressure chamber comprises a front body portion connected to the gas generator; an aft body portion connected to the front body portion and the gas generator; and a vent sleeve positioned around the front body portion and adapted to provide an aperture through which the gas exits the barrel in order to control a level of gas pressure in the barrel. A triggering of the gas generator causes the pusher cup to push the projectile out of the barrel at a predetermined launch velocity in order to attain a predetermined self-propelled flight trajectory, wherein the triggering causes the pusher cup to exit the barrel.