Bibbyman; To find a BP load for the .45 CS, use the normal blackpowder load development procedure.
Measure the depth that your bullet will seated within the case.
Fill the case with a suitable powder (FFFg I'd suggest) so that the load will be slightly compressed by the loaded bullet.
Other than that there isn't much else, other than to avoid petroleum products and lube the bullet with a BP compatible lube, like SPG, or Black Gold.
When I do that I come up with 21 grains of GOEX FFFg, for .45CS, .455 Eley (Webley Mk I) and .45ACP for use in a conversion cylinder.