I truly believe that for sizing all brass hulls you really need a full length sizer not just a ring. This could be lathe turned with a taper bore matted to give clearance for your chamber dimensions. This could be made up to fit a loading press or the hull could be simply driven in, lubed of course, with a plastic hammer or a regular hammer & block of wood & driven out with a dowel inside.
A Sizing ring sizes the same size all the way down & I personally would not prefer to size the base of an all brass hull down to the size needed to fix the forward end. Don't know what the chamber dimensions of this Patrick Mullin might be, but generally most shotgun chambers taper at a rate of around .005" per inch of length. I would simply not desire to size the base by that amount.
