Historically, the .45 Colt started out with 40 gr of real black; probably FFg, they seem to have used coarser powder per application than we do now.
Loads were soon reduced, some say cylinders were failing proof test, some say recoil was too heavy for the cavalry. Any road, they went all the way down to 30 grains, back up to 35 in the 1880s.
The .38 Special was special because it contained a whopping 21.5 gr powder charge and a monster 158 gr bullet... relative to the .38 Long Colt at 18 gr and 150, respectively. Loads varied by brand and era but that is the number I go by.
Modern drawn solid head brass is thicker and holds less.
It really doesn't matter as long as you don't leave a gap.
Non-gunpowder fillers are used for light loads to avoid airspace.