Here is my personal guidelines for guns that I'm not sure about:
Caliber size = minimum charge
2 x Caliber size = max charge
so for a .45 caliber gun use 45 to 90 grains of powder. Use either 2fg or 3fg, I would most likely go with 3fg in a .45 but every gun tends to have its perferences, or the powder I had on hand.
Hope this helps.