ORIGINAL: Chantecler111
And, energy does mean quite a bit in killing power, bullet diameter doesn't,
Wrong. Energy means nothing, but velocity does, so does expanded bullet diameters. The reason and only reason a .300 mag would be better than a 30-06 is out at long distances the 300 will still have the needed velocity for adequate expansion, Velocity=expansion=big hole. Bigger holes mean faster death.