RE: .308 Win
Caliber is in the eye of the beholder!!!
No matter the caliber, there are stipulations, rules and logistics that must be obeyed in order to make an "ethical and efficient" harvest. As long as you realize that the list of those observed restrictions is longer as you travel down the caliber ladder. That is to say that as the caliber and gun size increase, you have greater opportunity in the field. But with that comes greater responsibility! As many have stated here, some think that because they are using a big gun they can accomplish unbelievable feats of marksmanship.
My advice........spend an adequate time on gun and caliber but don't get overlycaught up in it. Spend more time learning to get"in amongst them"!!! The better you are at that, the less important the gunbecomes!