Over the weekend me and a co-worker of mine went to a gun show as he wanted to purchase a shot gun. Long story short he ended up buying a Mossberg 500 pistolgrip 12ga. He also purchased a Knoxx Spec. Ops Recoil Reducing Stock. We tried to install the stock on the shotgun but it does not match up to his reciever. Take it that the package of the stock says it is for the Mossberg 500. Has anyone come accross this problem. Any advice would be greatly appreciated. Thanks.