The diffence between lead and Bismuth is density. That difference means the same weight shot charge occupies different space. The difference in volume may yield radically different results or minor differences. This is why tested data matters. It matters more if you are on pressure limits with your load to begin with.

I am not saying you cant substitute Bismuth for lead with lead data. You may get an acceptable result, but without valid testing for pressure and velocity you are going on faith not fact.

I reference:
http://www.hodgdonreloading.com/reloadin...-reloading-data

Michael Dittamo
Topeka, KS