Elk are not that hard to kill if the shot is placed in the vitals behind the shoulders but I realize that is not always possible. So yes you need a bullet that will break them down as in big bones if the are heading for high ground. I took a large cow years ago with my 20 bore 320 grain dead soft round ball at about 1500 fps. It was a quartering shot from the rear but the ball was found in the front shoulder. It hit the shoulder bone hard enough to put her down. Of course it didn’t contact any rear quarter bones just a couple of ribs but even a big round ball is a killer. Select your bullets for the worst.

Rick