I’ve got a 6.5 CM in a Weatherby. It was an early model from them, so they actually put quite a bit of information in the box. According to them the minimum length for that caliber is 22”, with optimum being 24”. Which is what mine is. Mine is a strictly hunting rifle, with a taper profile barrel, and it routinely shoots one hole groups at 100 yards, from a cold bore. Hope this helps!