There is little doubt in my mind that the .308 is capable of killing an elk. Some even use a .243. With that being said, if the OP has a .338 that he is comfortable with and shoots well, why in the world wouldn't he take it?? By the way, the .338 was a derivative of the original .333 OKH originally developed by Elmer Keith an others soley for the purpose of elk hunting... but I'm sure some of you have never heard of Elmer Keith.