I'm assuming you want to use a round ball rather than shot, since you are shooting from a rifled rather than a smooth barrel.
If that is indeed the case, the best suggestion I would offer is to lower your powder charge to decrease meat damage and increase accuracy, then practice with that load at the range you think you will be shooting your hares at and at a target roughly the size of their heads (I don't think you would want to take body shots on hares with a .50 cal...yuck!)
I think you might want to try starting off with a 'starting' load of 50-60 grains powder, and then adjust accordingly.
Good luck.....and welcome to the forums!
