I loaded some black powder loads in .45 Colt for an engineer to evaluate, and can't tell you how many grains I used. I know that I checked the seating depth of the bullet, and allowed for 1/16" compression of the double F. Then I trimmed a case to use as a dipper, and had at it. Make sure you use bullets with a soft lube like SPG to keep the fouling soft.
Edit: I did check my measure, and it was 35 grains that I loaded.