Congratulations on getting the tag. 100 yards is a long way, but a roundball can do it. The .54 or .58 roundball would work fine. Your problem is going to be wind. But remember, most the time we hunt with the wind in our face when possible. So there the wind effect is not as drastic as you might think.

Both those calibers are more then enough for a deer. The whole key is as said, practice... Get out there and set up a target at some of the distances you expect, and then practice. Put one of them big roundballs through the vitals and that mule deer will not go far.

Good luck. I hope you get a chance at a monster. Can you use a scoped muzzleloader?