I have hunted with, and reloaded, bismuth for many years. Both waterfowl and the uplands when required. I rarely shoot at birds beyond 40 yards unless favorable shooting angle. My loads are between 1225 - 1250 fps. I typically shoot 1 oz payloads of #6 for early season smaller ducks and #5 for mid-late season larger ducks. Years ago I had a nice 12ga 1 1/16 oz load of #4 @ 1260 fps that was very effective on 40 yard birds but a little hard on the shoulder. Most of the time I just shoot a 1 oz #5 load @ 1225 fps.
