Actually Redding has changed their guidance. They used to suggest subtracting 0.002", now they suggest subtracting 0.001". Their current guidance can be found here
You will need more than one. What works best for you also depends if you intend to use the expander or not. If you use the expander, selection has more latitude. If you don't expand, you need to use the correct expander for your brass. If you convert to a carbide expander button, it will significantly reduce the effort to expand the neck, and reduce the risk of pulling the neck off center.