Your loading depends a lot on the specific brass. Some cases will load with conventional components, but others will require 11-ga wads. BPI (ballisticproducts.com) has the new Reloading Brass Shotshells manual by VanDenberg.
IIRC, there's an old formula for muzzle loaders that uses equal measures of shot and black powder. I don't know how this translates to shot shells.