I might consider using one for last ditch SD, as long as it went bang it would serve the purpose if reliable, but I would use the max charge for that, as you need every last bit you can get for that sort of function, I would think.
I will never understand why people have this notion that becasue its blackpowder shooting a lead ball, that loading it up to the max might just
get the 'job' done, in a SD situation. These things killed plenty of people in their day. I know i wouldnt want to get hit by one (or 6) of those balls, even if i was wearing a vest. Not to mention the sheer size of these pistols would make them damn scary to one would be crim that doesnt know a lot about guns. My 1860 Colt has a looooong barrel with a biiiiig hole in the end. Max load or not, being shot by one of these beasts will ruin your day.