Suppose you have the perfect shot, and make the perfect shot, but in the 1/4 second it takes your bullet to arrive, the elk takes a slight step? You hit 4 inches further back, and nick a leg bone on the way in, richocheting your bullet, with 30% of its weight gone, backwards and missing the lungs. Your elk runs off with no blood trail to become bear fat.
A .338, .45-70, or .300 magnum would have just broken the leg on the way in and dropped the elk in its tracks.
