Shot placement is far more important than any other factor. Any bullet with enough sectional density from almost any caliber will kill game quick with good shot placement. A 180 grain spitzer from any 30 caliber from 308 Winchester to the 30-378 has enough velocity to take North American Big game to 300 yards and maybe 400 yards. For one who likes the big magnums, they are there for you. For those who choose not to live with the Noise and recoil and muzzle blast, the 308 will do the job. The 30-06 has killed every game animal on this planet many times and will continue to do so where ever it is legal. Find the right bullet with 2500 fps and you will do the job. Likewise the 45-70 at 1800 fps with its big heavy slow bullet will also kill anything on this planet. Speed is not the only part of the equation as the 44 Mag with heavy cast bullets with even less velocity will also dispatch of about any critter. Check your history and see whats killed most of the game in Africa. We are lucky to have so many options available to us. The old mountain men would have been in heaven with our present day much scorned here 30-30.