Well, if a .50 or .54 lead ball won't do the job then it's probably not all that advisable to hit a larger animal with a smaller ball and expect good results just because it's hardened. There is a substantial reduction in ball size with their hardened ball.
Guess another bigger gun would cost more money, but then I've never been adverse to more guns.
Also, if a .50 or .54 round ball won't do the trick, a .50 or .54 conical should as long as it's short enough to stabilize with the twist of the barrel.
Hornadys hard ball looks like a product looking for a need. Kinda like that thing that tc came out with a few years back that was used to score round balls to make them break into four pieces. It seems to have dissapeared.