Part of the fun of CAS is picking the historical era you want to "live in" and dress up accordingly. Some of the guys live in the "gunfighter era" of 1865-1870 and look like a bunch of Civil War vets. Josey Wales, with Dragoons, '51 colts, and Yellow Boy rifles shooting black powder ammo. Others are in the 1890s, with top hats, pump guns, and Bisley Colts.
If you load BP in a rifle, you want to choose a bottleneck cartridge instead of .45 Colt, to keep some of the crud out of the action. Otherwise, .45 is fine IMO.
