A sealed combustion cartridge mechanism is used to propel a projectile and o ignite an impact percussion type primer which in turn activates a delay train located in the projectile. The forward end of a cup seal telescoping propelling member is axially dimpled so that it will hold the primer in close proximity to the delay train. The convex portion of the dimple protrudes toward a movable propellant cup slidably contained within the closed combustion telescoping member. The propellant cup upon ignition of the propellant is forcibly thrown, by the rapidly expanding gases, against the protruding dimple and the rear of the projectile. The kinetic energy of impact of the propellant cup against the dimpled surface of the telescoping member is utilized not only to help the expanding telescoped cup seal member drive the projectile from the cartridge, but also to ignite the primer and start the delay train of the propelled round.