I have 2 of them that I built. On paper there isn't much difference between the .22-250 Imp and the .22 CM. I've had both and the reality of the deal is that there is that the CM case has just enough more case capacity to reach another tuning node above the .22-250 Imp. It's good for an additional 200 fps or so, depending on the individual rifle, powder and bullet chosen. That's not a huge advantage, but it's definitely there. There are quite a few of them around here so I get to see a number of different set up and loads. The biggest mistake I see made is assuming that a powder that is appropriate for the 6.5 CM is also good for the .22 CM. It's important to remember that a 6.5 barrel has aproximately 35 to 40% more bore volume than a .224 diameter barrel (depending on the land/groove number and rifling geometry). With the same cartridge case size you need to use a slower powder with the smaller bore than you can use with the larger bore. H-4350 is a good powder for the 6.5 CM but will reach unacceptably high pressure before it reaches optimal velocity. You will see .22 CM rifles that shoot good groups with 4350, but they do it at lower velocity. The higher velocity accuracy nodes have always yielded the best accuracy. It's a great cartridge that is a real performer if loaded correctly. Build one, guarantee you will like it.