Meanwhile , while I was typing above :
Yes pellets are BP substitutes , typically Pyrodex , sometimes 777 .
They were developed for shooters , primarily with inline rifles , who use them primarily for hunting . More convient to use in the field w/o dealing with flasks and powder measures .
Available in both 50gr and 30gr equivalents , most commonly 50 . 2 50gr is considered a standard load in .50 cal ML , 3 50gr a " magnum " load , for rifles so designed . 30gr allows fine tuning charges , to say 90gr or 120gr
Hogdon Does list a loading for a 30gr pellet in .45 Colt . , and for .44 cal C&B revolvers.
BUT , pellets are considerably more expensive than loose BP . If you only hunt with minimal sighting in , a 20 pellet box will last all season . Likewise C&B Revolver owners who just want to try them out , can buy a box of pellets , and not invest in flasks and measures .