I asked the owner what the point blank range or trajectory curve was with that load and he replied:
According to my round ball ballistics calculator, if it was sighted in at 25 yards, the ball would hit about 9" low at 50 yards. If sighted in at 50 yards, it would be about 4 1/2 inches high at 25 yards. My guess is that they were sighted in at around 50 yards; these large balls were for stopping someone quickly at short range.