Basicly, CAS is as period correct as you want it to be. Me, I shoot period Military weapons, in period military calibers, Black powder loaded, wearing period military clothes. 'Cause I like it that way. Next feller in line might be in Jeans, chambray shirt, straw hat, with Stainless steel rugers in .357, smokeless. I pick up his brass, he picks up mine, we slap each other on the back, laugh at our mistakes. We're both having fun. The basics are the same, we're both using single action revolvers, lever action pistol caliber rifles, and the proper shotguns. Everything else is simply details
The details are up to you.