Critters have gotten tougher to kill over the years.
These days you need a magnum, while years ago the venerable 7x57 killed a thousand elephants in the hands of a superior shot.
Lets crunch some numbers. A 308 will push a 180 grain bullet at 2500 fps. A 30-06 will drive a 180 grain bullet at 2700 fps using a very moderate pressure load. A 300 WM will drive the same bullet at 3000 fps.
What does this really mean? Obviously the 300 WM has more energy and a flatter trajectory. The 308 developes 2498 ft-lbs. The 30-06 driven bullet has 2913 ft-lbs of energy at the muzzle. The 300 WM driven bullet has 3597 ft-lbs of energy at the muzzle. Basically, the 300 WM has as much energy at 100 yds as the '06 has at the muzzle and about the same as a 308 has at the muzzle at 250 yards.
How much flatter trajectory? Lets assume the rifles are zeroed at 200 yds. The 308 bullet will drop 10.2" at 300 yds. The 30-06 bullet will drop close to 8.5" at 300 yards. The 300 WM bullet will drop 6.7". At 400 yds the bullets will drop 29.4",24.7", and 19.4" respectively.
What does this data really mean? If your using either a 308, 30-06, or a 300 WM and it is sighted in at 200 yads.....You better have a range finder and know your drops if your shooting at anything much past 250yds. If you dont, your risking a wounded critter instead of a clean kill.