Ed you are planning to build a single barrel 4-bore? Gutsy move even I ,with my love of recoil, would not want to hunt dangerous game having to work any action before a follow up shot.
But seriously thanks for the barrel tip!! the bullet your going to use is a little heavy but what the #### better to over kill then be killed.

I kinda had planned to machine my own brass, its an excuss to get out of the house But I would be interested in your adaptation of 20mm brass.

sound like a real time saver.

Recoil Builds Character!!!