I also make my own bismuth shot now, and have been shooting it for I think 4 years now. I grew up knowing only steel shot on ducks. I've tried some others like Hevishot, but never got to use it enough because it was so expensive. I finally decided to try bismuth, and have not shot any steel shot since. I killed plenty of birds with steel shot, and still could. That said, it is ridiculous how ineffective it is once you try a better shot like bismuth, and I can only imagine how lead was. I was worried about the cost, but the real eye opener was how much less ammo I go through. In the past it was nothing to go through a box a day, and still not come back with a limit. This year has BY FAR been the best duck season of my life time. I whiffed on opening day and ended with 4, otherwise I think I had a limit every single trip in October. That is 11 days hunted, and 64 ducks recovered. I only fired 85 shots to get them. I had loaded 100 shells before the season, but never had to load more! This was not a muzzle loader, this was a Benelli nova at first, before I went to my Mossberg 500, both with a full choke, and my 1 1/2 oz load of #4 bismuth. I also did a trip in ND, but not so much for ducks, I was after a tundra swan. I did end up shooting ducks, I even got 2 nice canvasback with a single shot from my Ithaca Mag10 and 2 oz load of B (I have to buy size B). When I finally got in range of a swan, I took a single shot, and the swan was stone cold dead in the air.
Making bismuth shot is exactly the same as making lead shot, just with a lower temperature. I use a Littleton shot maker, but had to go off script to make #4. I keep hearing that you can make bigger shot by using a lower temperature. I have a PID, and can precisely control my temperatures, but could never get it to drop more than a 1/2 size bigger than the dripper was drilled for. Instead, I bought a numbered drill bit set, and had to drill them bigger until they were dropping where I wanted. I could not get good round shot bigger than about #3. I do have a buckshot mold for BB, and may try that next year.
As for sizing, I started with #5, and have also tried #6, #4, #3.5, #3, #1, and #B. I shoot mainly small to medium size ducks, and found #5 worked well there, but I found I was wounding some bigger ducks. I found buffer is a key component for tight patterns, and with a tighter choke, these loads are incredible. I found that with #5, I had plenty of pellets for even 65 yard shots, but at that range, pellets would only go through the one breast, but not into the organs. I found #5 really only worked well to about 45 yards. I'm not a velocity fiend, I have not found velocity to play nearly as big of a difference as people give it credit for. My 1 1/2 oz load is running about 1300 fps, when measured in the summer, likely 1250 fps in the cold. I switched to #4, and found they would penetrate all the way through a good size mallard at 50 yards, measured with a rangefinder. Depending on if you count holes right on the line, this load patterns 75%-80% in a 30" circle at 50 yards from my Mossberg 500 with 30" full choke barrel! This is ok, as teal and wood ducks are a small target, and could easily slip through a pattern much thinner. I consider 55 yards max on that load. #3 would not be a horrible choice either, and I am considering going to it. They penetrate through a duck a LONG ways out there, longer than I'll shoot.
For geese I started with B. In the past, I've never seen a goose flat out killed with any steel shot. I settled on BB steel, but many in my family shoot BBB. I've also seen them brought down with #2 and #3 duck loads, as well as my experimental T shot loads. In no case has one ever been dead on the ground, they are always broken wings or body shots that were not instantly fatal. I'm sure the occasional head shot can happen. I think it was opening day when I was first using bismuth, and I had my 10 gauge with B shot, a nice goose gliding by at about 40 yards. One single shot, and it flipped over dead, feet kicking in the air. My mouth dropped, I've never seen anything like it. Thankfully that story has continued, as most geese shot with B bismuth have been one shot and flip over dead. I did try #1, but found it did not penetrate enough at any real distance. B shot works to about 60 yards, which is also about where the pattern is too thin.
So for me, where duck hunting had been extremely tough, and 90% of the shots I got were 40-60 yards, bismuth was a game changer. This year, ducks were flocking right to me, and many shots were only 20-40 yards, I likely could have done just as well with my old #3 steel shot loads. Next year could be another grind, where I'll appreciate the range again. I will say that at ALL distances, bismuth has been a game changer on geese. I've never shot a swan with steel shot, but I wouldn't want to either. Those things are huge. I shot one last year in SD, one shot with B at a little too far 60 yards brought it straight down. This year in ND, one shot at a more modest 35 yards had it flipped over in flight. Since pellets pass clean through a bird at closer ranges, the extra damage is not that bad. I will say B shot leaves a large hole in a duck breast.
If I were to shoot my Pedersoli for ducks and geese, I would not use anything besides bismuth shot.