The old muzzle loader's mantra was 'Little powder, much lead, shoots far, kills dead!'
As for cartridges I went to the local black powder shoot (only about 10 or a dozen show up on a good day) and as it was a rainy day I though I would be a bit lazy and took along an old Harrison & Richardson 12 bore single and some Baikal cartridges that were supposed to be for 2 1/2" chambers. Number six shot but load not specified but I suspect 1 1/8th. ounce. I'd had them (stored correctly) for about 40 years. My goodness they were tooth rattlers. What the velocity was I have no idea but they bust the clays; in fact they just pulverized them! Fearsome things that I certainly would not use in a 2 1/2" chambered gun. I still have about 180 left. Any takers? Lagopus.....