Bull, over the years I've probably owned and shot over 20 Damascus barreled SXSs. I normally shoot low pressure nitro loads, but on occasion use BP. We go to SxS Shoots and my friend or two and I like to use smoke. Those are usually 100 to 150 shots in one day. And then there are times at my local club I use it. I like to loan someone a shell if they need one. My buddy was shooting two shells at a bird in skeet if he missed the first shot. Well, about station six he was gonna run out so I offered him one of mine. I didn't tell him it was BP, just said it was guaranteed to smoke the bird. He was shooting a ported Browning O/U, and it was almost dark out. The gun want off, flame came out of the porting, he kind of tossed the gun up in the air thinking he blew it up. I can't repeat the language he used but it ended in he'd never ask me for another shell. I know when I shoot trap or skeet with BP the other shooters always complain about all the smoke stopping them from shooting. Fun to watch em whine.
I throw a SxS Shoot each year since 2005 and a old guy with a handlebar mustache and period correct clothing would show up shooting BP in a 10ga hammergun. I never ask what his load was, but the ground would shake and he'd laugh like hell whether he hit the bird or not. Man, did he ever enjoy himself.
It's kind a hard to over do it with BP in a shotgun shell. One normally loads by VOLUME a equal part of shot to powder. Along with all the wads it's almost impossible to load too much powder. Those adjustable measures for a couple of bucks [ todays in plastic, the old ones at gun shows or maybe Amazon are brass with a wooden handle ] have drams and ounces of shot marked on the side. 2 1/2 drams of powder [ one dram equals 27.3 grains of powder ] and 1 oz of shot, 3 drams and 1 1/8 oz of shot, and so on. The rest of the space is a OP card and cushion wad to get the proper load height for a good looking crimp. The old duck hunters used all brass shells. They'd have a shotbag and powder flask slung over their shoulders, some wads and primers in a bag along with some extra brass shells. With a couple of simple hand tools they could reload all they needed for a day or two of shooting. I have all the old tools and a couple of 12 and 10 gauge brass shells I keep around just to look at them thinking of the stories they could tell.