King,
I did a lot of patterning Bismuth many years ago, 28 gram loads at 1200 to 1300 fps from old, long-barreled, tight-choked 12 and 16gauge hammer doubles, IMR SR7625 powder Rem SR16 or Remington 12 gauge wads, Federal or Remington hulls and primers, chamber pressures around 9K psi. I did see a few pellet fragments but not many -- patterns were 80+% at 40 yds, not much room for missing many pellets. When I clean ducks and geese shot with bismuth, I do, sometimes, find a few pellet fragments, some seem result of hitting major bones. Most are intact, round pellets.
I do hear that initial bismuth shot as nearly pure Bi, which is brittle. My bismuth shot is from later, when Bi was alloyed with tin (Sn), which gives a much less brittle metal.
I also suspect that when firing heavy waterfowl loads, say with 1,5 or more oz of shot, that more pellets fare badly than in my 1,0 oz loads. I see no need for such loads.
I have never had much success killing cripples at longer ranges with any kind of shot -- much too small kill zones relative to pattern density and pellet energy. Actually, I seldom have any cripples, thanks perhaps to taking only shots I feel confident about. Typical hit with Bi-Sn results in ducks folding and only twitching and flapping some after hitting water.
After 3-4 years of shooting both Bi-Sn handloads and Kent TM factory loads on ducks, from big mallards to green winged teal, I settled on Bi-Sn for everything. Well over 50 ducks with each type of shot. I do have a few boxes of heavy 12-70 TM loads, with 36 grams #3 shot at 1450 fps(!), but have never taken them goose hunting or a gun suitable to shoot them in. Also have one box of TM 12X67, 28 grams of #5, 1300 fps loads but they are never in chambers when geese come by -- 28 grams of #5 Bi-Sn have been doing a string of 1-shot kills.
Probably next time I go pheasant hunting I will use 28 grams of #5 Bi-Sn. On last trip I used 28 grams of #6 lead (Remington Game loads, 16X67) and none of long birds (roughly 40 yards) came down dead, even with 6-10 pellet in them. Dog had to find them.
Niklas