decades ago when I was doing it, Black Powder shotshells were always loaded by drams, NOT weight.
A certain volume (in drams) for a given weight of shot. What the shot size was didn't matter. #8s, #4s, or buckshot, all the powder cares about is how much weight it is pushing.
measure the weight of how many 0000 balls fit in the case, plus weight of your buffer and use the proper dram equivalent of powder for that weight.
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All else being equal (and it almost never is) bigger bullets tend to work better.
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