Abstract: A projectile propelling system includes a gun barrel filled with a gaseous propulsive mixture, a projectile having a front cone wall and a rear cone wall, and a driver for initially propelling the projectile in the gun barrel to an initial velocity above the detonation velocity of the gaseous propulsive mixture to produce a shock wave at the front cone wall followed by a detonation wave resulting from the reflection of the shock wave inside the barrel, which detonation wave is applied to the rear cone wall to increase the velocity of the projectile. The front cone wall and rear cone wall of the projectile are such as to create a "mach stem" in the form of a disc normal to the longitudinal axis of the projectile, of sufficiently high pressure and temperature to ensure ignition of the gaseous propulsive mixture.