I don't have anything to go by as this is the only RM kit I have. I know that the stock AM kit that I have fits totally flush with the bottom of the rail and so does the XM15 kit. I did get a PM back from him saying that he thought the rail channel might be too narrow since his pump rod/arm whatever is thicker than the AGD one. I personally don't think that's it. When I pull the assembly apart and slide the pump arm in and out, it slides freely. As soon as I put everything together and snug up the front mounting screw it binds.