With black powder, modern steel barrels wont burn enough powder to case any harm. They just blow unburned powder out of the muzzle. So over loading one is just a waste of powder and there is no benefit in loading max loads. You run into the wall of diminishing returns. It doesn't take a heavy load to kill game. My 50 caliber rifles will exit deer with 60 grains of powder, every time. Accuracy diminishes as you approach maximum loads as well.
When I work up a load for a hunting rifle I start with a "Square" load (50 grains in a 50 caliber) and work up until my groups begin to open up. That's where I stop.
