Lots of things unstated, undefined here. I have used bismuth loads of #6, #5, #4 and #3 at about 1200 fps and killed even big mallards cleanly at 30-40 yards. #5 and #3 at 1300 fps kill big geese cleanly at between 40 and 50 yards, often with too many #5 pellets in bird.
Pattern density: In my old guns with tight chokes, bismuth shot patterns very tightly, often 80% or more. Point it just right and dead ducks and geese fall.
In my old doubles, lead and bismuth loads shoot to same POI, and same for both barrels. With tight bismuth patterns, a wayward POI could be bad news.
Niklas
