I have an XM-15 and was trying to alter the elevation wheel setting in accordance with RIBZ guidelines and discovered that Bushmaster made the elevation wheel on their ARs has one machined piece. It's not mil-spec. A gunsmith recommended that I replace the whole carry handle (instead of the impossible to find elevation wheel part, as I was initially going to do) with a precision built one that is mil-spec. He suggested perusing through discussions at High Power Shooting forums as a good way to get a lead on manufacturers. What are the best High Power Shooting forums.