Re: 300RUM or 338RUM? Which and why???
Muzzle velocity is an important factor when determining recoil in approx ft/lbs, but it is only one of the factors. I would suggest you download Pointblank ballistic software if your current software doesnt calculate recoil. Its free so you dont have anything to lose.
The recoil between a .300 RUM and the .338 Ultra mag (any ammo for that matter)has to do with the weight of the gun, the grains of powder, grains of the bullet, and the muzzle velocity.
So you can see that depending on any of the four variables, you can change the felt recoil. Pick your gun and ideal cartidge for both and then plug in the numbers. Have fun and good luck!