Most bismuth I've seen is round like lead, & without all the deformation at setback & through choke constriction, my experience has been that it patterns a hair tighter than unplated or even copper plated lead on average. Depends somewhat on the gun/load/choke combination. The exception would be Hevishot's bismuth. Some of it was sort of egg shaped, or even tear drop. One more reason it's inferior, in my view, & I make use of my opportunities to give it less than glowing reviews. Hevi really pissed me off.
Experience has also taught me that if you're ready to shoot a rooster at 20-25 yds, you shoot it, because it's likely your best shot. So I best be somewhat appropriately choked. Waiting not only increases the chance of a cripple, it increases the chance of a miss, neither of which are good things. For me, anyway. Waiting allows my active brain a chance to become too involved.
My videos have shown something I find kind of neat. I typically feel reasonably calm when shooting a rooster. But on birds when I actually recall thinking, "Oh, I've got time on this one. I'll wait a bit," the videos reveal that the shot process still happens very quickly & that if I wait at all, it's only for a matter of 5 yds or so (10 max). Those birds usually die hard deaths. I think the explanation is that these are usually, strait-aways (or nearly straight-away), which don't permit shot penetration as well as a more crossing type angle. In super thick cover, it's unwise for me to take a straight-away past 35 yds or so. Not hard to put 'em on the ground, but recovery becomes less likely, even with the most experienced dogs. I suppose if I hunted with a pointer, I'd see more real close straight-aways, & therefore more waiting. Especially if I "hunted" flare nares that'd just been released that morning & needed the persuasion of a boot in the ass in order to take flight. Fortunately, I'm able to hunt only the wildest of the wild, and a flusher fits my needs/style best, so waiting is somewhat uncommon.
Interesting how different strokes work for different folks.