Well if you refer to an 1873 Colt model P, Also Known As the Peacemaker, it was only safe to load 5 rounds into the cylinder if you were going to carry it. Sometimes called "five beans in the wheel" If 6 round were loaded and the firearm was dropped onto a hard surface on the hammer, you ran a pretty good risk of it firing. Not a good thing. Of course modern revolvers are safe to load 6 rounds into with their various safety mechanisms like transfer bars. So your "sixshooter" was really only a 5 shooter if you wanted to be safe.