"substituting Bi for Pb by volume (as MOST of us do with our reloaders),"

Quite the statement and assumption! Seriously dude.

"I can't quite see how different powders are going to greatly change the safety issue between Pb and Bi loads. What principles would create such differences?"

If you can't quite see the differences in powders.....well I'm glad I'll never be shooting beside you and your hand loads.

Best wishes and good luck.

Life is too short to have a 'hate on' for so many things or people. Isn't it?