If memory serves, I've watched 8 elk die via .308 with various standard construction bullets and about 20 with the .300 Win Mag (plus two red stags) with the same general types of bullets, at short to mid ranges. Nothing real big mind you (save one red stag)....mainly rags and cows. I can honestly say I noticed zero difference in the killing effectiveness between the two rounds.
I got over my magnumitus when I was about 30-32. I just have no desire to shoot those big boomers anymore. The two red stags I shot with the .300 Win Mag were with borrowed rifles...else I'd of used something significantly smaller.
