While a .62 caliber with the right rifling might be nice, I would probably just go with a .58 caliber. After all you are going to be shooting roundball. You are going to get as close as possible. You are going to be careful in shot placement. 284 VS 324 weight difference, and then the difference in diameter. A .58 is a big ball. If that expands at all, think of the hole that will be knocking through the animal.

Now I have to admit, if they offered the .62 in a rifled barrel I would get one of them, just for the thrill of shooting it and owning it, but that .58 is a good caliber. The early mountain men in the Rockies were happy if they had a simple .50 caliber Hawkins. They would have been thrilled to death to get a .58.