An advanced Tactical Stock System for the Mossberg 500/590, 12 gauge shotgun. It utilizes a proprietary, lightweight, carbon-fiber reinforced polymer, impervious to weather, and is able to withstand all standard gun solvents and oils. A six-position, collapsible butt-stock allows shot-gunners of all sizes to find the optimum adjustment for fit and comfort. A 7-round shell holder mounts to the left side of the receiver and includes individual shell-retention adjustment for each round, without interfering with the stroke of the forend.