Hi Robert. I use a .32 cal Traditions Crockett to hunt rabbit. I use 20 gr. Pyrodex P with a roundball. That being said I have also used a CVA Bobcat .50 cal with a roundball and 25 gr. Goex 2F. You must hit them in the head with the .50. I caught one in the hind quarter and there was nothing left.
Have fun and enjoy.