You don't really need one on a 6.5 CM for hunting applications, unless you're extremely recoil sensitive or you're going for an ultra light rifle and need to mitigate every bit of recoil.
The 6.5 doesn't recoil that much even in a lighter rifle. Muzzle breaks are most useful in competitions where you need to stay on target for multiple shots, or to spot your hits. I shoot a 8 pound 308 with 165's 40-50 shots at a time without a break and the recoil isn't that bad.
Also it gets LOUD, so unless you hunt with ear pro in a break will make that otherwise moderately annoying single shot into something extremely uncomfortable and unpleasant.
Maybe have the smith thread it for a can if that's legal in your state? Best of both worlds because you get some noise reduction and some recoil mitigation.
But if you really want a break, the apa gen 2 and the Alamo 4star offer the most recoil reduction, imo.