Abstract: A cartridge case closure plug for closing a cartridge case, enhancing plug reakup in the shortest time span after ignition of the cartridge, and substantially reducing plug mass to reduce the impact loads exerted on the projectile by the plug. The plug is cylindrically shaped and constructed of a polymeric foam which may be covered with an elastomeric coating to lower the permeability of the plug. The plug is provided with a forward face, a rearward face and an outer cylindrical surface. The forward face of the plug is furnished with a centered depression which allows for center blowout and breakup of the plug upon ignition of the propellant contained in the cartridge case. The rearward face of the plug is provided with a tapered cylindrically-shaped cavity which reduces plug mass and enhances plug breakup while reducing the impact loads on the projectile.