I hunt once in a while for the ML season on local Blacktails which are small deer, and keep it well under 100 yards with .50 round ball and as said they work OK with good hits. I use a .50 Lyman Plains pistol as back up and shot a couple over the years with it which were not quite finished and from 50 feet or so it produces the same wound as the rifle at 50 yards and works quickly and humanely. If I wanted to stretch it I use a modern rifle, I want a quick, humane death for the animal..
And the plethora of hunters on the traditional forum claim just that out to even 125 yds.