The invention is an improved load bearing arrangement for use with firearms. The system comprises a cylindrical body with a sealing cap, mounting structure on the body including a plurality of mounting tabs and a "T" rail with matching structure on the stock. The mounting tabs are only partially fastened on the body so as to form hooks which will secure the body from behind the structure on the stock. The "T" rail interfaces with a corresponding notch on the rear of the stock and is secured with the stock's butt pad. A water-tight cap is also provided, which is also capable of removal and replacement without removing the remaining structure from the stock.