First keep in mind that the 45 Colt loads that were with 40 grains of powder were loaded into balloon head cases which hold more powder than today's cases.
I shot the 45 Colt with BP for a few years in SASS before going to the 44WCF.
A very easy way for a new shooter to get his feet wet with loading real BP is to use the following system to find his load.
Take a 1/4 inch piece of dowel rod and lay your bullet on it's side. Put the bottom of the dowel even with the bottom of the bullet. Now go up the dowel and when you get to the crimp groove put a mark of red ink or similar mark at this spot on the dowel. Now fill the case with 2F powder until you can put the dowel into the case and barely see the red mark over the edge. This will be your correct load for that bullet. Weigh the charge and record the weight so that you may make your adjustments on your measure.
Remember that all BP brands and lot numbers will be different and you have to reset if you change lot or brand.
To give you a good example is the Swiss powder which is finer in grain size that the Goex of the USA. In fact almost all black powders have different sizes when you compare the USA powder to them.
The posting by Jim Watson is I'm sure an typing error on his part as the gun powders of the mid to late 1880's were finer in size and not coarser as he posted.
All BP is the same with the difference being in the grain size and shape of the grains. All BP burns from the outside surface in. If you have a very smooth and even shaped grain then it will burn faster than one that is all irregular and rough on it's surface. Glad to see you on the Fun side of shooting. You will most likly find your loads to be some where in the 33-35 grain area.
If you choose to shoot lighter loads then just use the 45 Schofield case with a 200 grain bullet with the revolvers. The loads are about 26-28 grains. Very fun to shoot.
SASS Frontier Cartridge class, 100% BP Shooter,