http://www.hodgdonreloading.com/relo...reloading-data
Matching Shot Type and Size to Reloading Data
It is easy to assume that all shot types can be reloaded similarly; after all, they look the same – being round balls of metal. However, in loading shotgun shells, this assumption cannot be further from the truth.
The two characteristics of shot that change reloading data are shot hardness and density.
Shot hardness has a direct effect on chamber pressure. Softer shot produces lower pressure; harder shot raises chamber pressure dramatically. The softest shot type is lead. The hardest shot types are steel and tungsten. Bismuth falls between lead and steel. This is the primary reason that lead shot reloading data can never be used with any other type of shot.
Shot density affects how much room in the shell case the shot charge will take up. To try to simplify shot density, think of it this way:
A coffee cup of steel shot weighs less than a coffee cup of bismuth shot
A coffee cup of bismuth shot weighs less than a coffee cup of lead shot
A coffee cup of tungsten shot is heavier than all the others
Just remember, in shotshell reloading the reload data must be specific to the type of shot being used. Hodgdon reloading data meets this requirement.