Depending on the range, a .54 can and has harvested about anything in North America. The 224 grains roundball is a lot of lead. With the right powder charge I would not worry about moose. In fact, on a different forum they told of a person shooting a moose with 90 grains of Pyrodex RS and a .54 caliber roundball. The interesting part is the moose was 160 yards away. The ball still was able to penetrate into the heart causing the death of the animal. Now I am not saying shoot that far at animals. I would never suggest even such a thing, but 100 yards, and a well placed shot, and you can penetrate about any critter you want to tackle.
I had the experience of shooting a .54 roundball with 80 or 90 grains of Pyrodex RS at a deer standing 80 yards away. The ball passed through him dropping the deer where it stood, and struck and killed a second deer I did not see some 15-20 feet behind the first one, breaking the spine of it, and knocking that one flat as well.
Roundball are a good hunting projectile. The big thing with them is make sure you place your shot. The ball will do the rest.