Ergo Grip Tactical Stock Adapter, Fits Mossberg 500, 590, Black 4454 Use ERGO's Mossberg 500 Tactical Stock Adapter to install AR-15 type stocks and pistol grips on your Mossberg 500/590 shotguns. It can be used to shorten the length of pull on your favorite scattergun to a more manageable length. Any standard AR-15 grip will also bolt right on" further increasing ergonomics.