Re: .300 RUM muzzle break???
I shoot a 300 Jarrett with Kenny's brake, a 300 RUM with a Vais and a 338-416 Rigby with a Vias. The 338 is loaded with 119 grains of H-870 behind a 230 grain slug. None of these rifles are light weight (they will all weigh in the neighborhood of 10lbs or more), and yet none of these rifles kick as hard as a 308 Ruger that my son has. The Ruger has the "skeletonize" stock and doesn't fit anyone but a child - yet IMO the 308 manages to kick like a Missouri mule.
All of this simply testifies to the fact that there are a lot of factors involved in recoil; Stock fit, effective muzzle brakes, caliber and weight of the rifle, muzzle velocity - and maybe most important individual perception/reaction to recoil.