I read a book once about a fellow that always hunted deer with his flintlock. He used the "same powder to prime as to charge," so I am guessing he was using 50 grains of FFFg black powder and a round ball. His thought was he did not want a pass through. Instead he wanted the ball to release all its energy inside the body. (I personally think this would still get pass through but might be wrong) He claimed in his writing that this was good to 100 yards.
I have to disagree with his reasoning and tend to lean towards the other views here. I like to push the load to the near max when I hunt. In my .50 caliber sidelocks, I use 70 grains of FFFg. I have found that with a roundball I can still break an animal down to plant them better, and I usually (last year was a real puzzle) get full pass through.
But instead of telling you what the minimum load might be, I would suggest find out what your most accurate load might be. (Unless this is for a very small person, then you might have to take charge into consideration) and that would be my hunting load.