I tend to agree with the better comparison being .243 vs 6mm CM. Case capacities and velocities with approx. equal weight bullets are similar for both rifles. .243 is basically a .308 case necked to .243/6mm. I guess it could have even been named 6mm-08, like its slightly bigger brother the 7mm-08 (which I prefer over them all). I built my Grendel because I wanted something with better legs in an AR-15 than .223 offered. For a bolt gun, I'd take either 7mm-08 or 6.5 CM.