Getting back to this velocity test. Did you compare patterns as velocity went up? Wondering if the pattern started to blow apart with the increased velocity.
Well I half heartedly tried to test this somewhat today with no real correlation. I started with 1 card wad, and got horrible patterns, then 2 was decent, 3 was very good, 4 was very good. The load was the same 100/100 load of Goex F and #5 lead. I then started testing bismuth #4 with the same 4 card wads, but varying the powder. With lead, I often saw patterns start to degrade at a certain point. It did not seem to be the case with bismuth today. With a 100/100 load (powder/shot by volume) I set my baseline. I then started going up in shot 100/110, 100/120, and 100/130. I have yet to calculate the pattern %, but eyeballing it, more shot put a few more holes on paper, but all were surprisingly good. I then tried 120/120, which looks as good as anything. I then tried more powder than shot, 120/100, with little change in pattern. I then went all the way to 140/90, and while less shot on paper, I'm betting the pattern % will be pretty close to the rest. I would not feel bad about any of these for ducks.
This was in my 10 gauge SXS, and it seems like it loves #4 bismuth no matter what I do. That's the thing with patterns, you never really know for sure what will work, and what wont. Over the years you get better at it, and know what doesn't work, but people have spent their whole lives studying shotgun patterns, and never found a perfect correlation to any one thing.
Then I tried #B bismuth, and while decent, I did not get anything to pattern in any way I got excited about. It would probably kill a goose at 35 yards, but at the 42 yards I was pattering at, it would be iffy. That's another example of the oddities of patterns. Maybe I haven't found the right combo, maybe it doesn't like B shot. I have a BB size mold to cast some bismuth shot, which I plan to try some day.
Then I tried some buckshot. Generally the large sizes of buckshot pattern very good. This did not seem to be the case here. The largest I had was 0000 (.380"), and this gun does not like that size. This stacked in very tight 3's, which is often not a good combo for whatever strange reason. Stacking in 2's seems to work better, which in this gun's .804" bore would need 00000 buck. I believe I do have a .395" mold. Anyway, the usual 4 card wads with this 0000 buck produced horrible patterns, and an off sounding report. Recovered wads showed they may have been leaking by. I theorize it was because so little of the buckshot surface area is on the wad, it is not supported well. I went all the way to 8 cards, and found improved patterns, and a strong report. Recovered wads still showed a waviness. I then figured something to take up the open space between the shot may help. I went back and cut some 1/8" felt wads. I then loaded 6 card wads, and 2 felt wads. This seemed to really help. Patterns were the best this way. I had been shooting 9 pellets. I then upped it to 12 pellets, which really seemed to help, but I still wouldn't trust it for hunting.
Instead this gun really seemed to like 2 buck, which is .270". It stacks nicely in 7's. I found 100 gr powder, and 28 pellets would be very lethal to a deer at 42 yards.
So forget the year I quoted earlier. I don't think I'll ever know the answer.