208 through an inlet 214 the inlet is located in front of the last projectile 216 in the firing chamber when the propellant enters and or is ignited the pressure from the propellant forces the projectile 216 against the projectile retention device 212 which helps to substantially seal the second opening of the firing chamber once the pressure from the propellant becomes so great the projectile 215 overcomes the resistance of the projectile retention device 211 and the projectile 215 is expelled out of the firing chamber 208 and through the barrel of the gun as illustrated in fig6 d the retention device 212 then deflates dilates and the next projectile in the storage magazine is introduced into the firing chamber moving the projectile 216 up against the retention device 211 and the gun is ready to be fired again furthermore the gun may also comprise means for detecting whether the gun is in a proper firing condition these means may include mechanical sensing means for detecting projectile pressure on a retaining device e g projectile retention device 211 or means for detecting occlusion of a light path not shown according to one embodiment of the invention the gas or air expelled from the retention device 212 during deflation can be directed through an.