Small doses of ball powder, air space in the case, and consistency do not mesh. Won't happen. Too many variables. Light loads you still want to fill up that case (and not with air.).
All of my light loads for 38s are using Unique powder. Most of my light loads for anything are using Unique, but that is only because of 30+ years of experimenting and always going back to what actually works.
Unique, Trail Boss, Clays, Universal Clays, etc are what you are wanting. Small dose fills more of the case and does create consistency AND accuracy.
Steve