The .243 Win already has plenty of Umph for deer hunting. If you want more energy, go to a larger bore or bigger case. Regardless of the posts doubting the .243 Win ability, as drdougrx related, there are other posts where the majority applaud this round for deer. I, for one, with lots of personal experience trust the .243 Win with APPROPRIATE bullets used on the game intended. It includes black bear, white tails, black tails, caribou, sheep, goat, mulies, and one average elk. All were well hit and no animal ran far once hit. But again, use the proper bullet for the game intended.