Abstract: A shotgun cartridge system includes a shotgun shell and a detachable cap. The cap fits within the casing atop the open end so as to close the casing and prevent the projectiles from falling out. An edge recess on the cap enables finger-nail removal of the cap. An injection port enables injection of a coating substance onto the projectiles. The inside wall of the casing may have a projection to snap connect the cap in the casing. The cap then has a mating projection recessed into the cap-wall and structured to snap in place below the projection on the casing when the cap-wall is slid into the casing. Alternatively, the projection is placed so as to form a thread around the inside wall and the cap's mating projection engages the thread when the cap-wall is slid, rotated and tightened against the thread.