every gun is different but I would bet 80 gr. would probably be the most accurate

50 yards shooting roundball anything over 70 grains of powder will do fine. I normally like as powerful and accurate a load as I can get so I get best expansion and pass through. But there is an old school of thought and old timers used to believe they did NOT want the ball to pass through. Instead they wanted it to enter, expand and release all its energy in the body cavity. Whether I agree with that or not makes little difference.

In one book I read, it talks about a 50 grains charge with a roundball as being the best deer load out there. Again, their thoughts were... accurate, the ball hit vitals, and expanded. Then it stayed in the body and released its energy.

The big thing is accuracy. Put that roundball in the right spot and you will have your deer.