OK, don't ask me how I know this!
I was going to see if I could download AA#5 to AA#2 velocity levels. The cartridge was the 38spl. After firing one shot at those reduced levels, I had a squib stuck in my barrel. I cleared it and shot another with the same results, pulled the rest.
All powders have a range of effectiveness. The lower levels are part of a recipe as well as the top ones, period.