If using a chamber reamer, how would you bump shoulders and size the body slightly under chamber dimensions to ensure proper feeding and extraction?if you own a custom chamber reamer just buy a die blank and let your smith go to town, Whidden sells replacement plunger kit or let your smith make his own and you have a hydraulic form die likely faster and cheaper than a one off made on a cnc lathe.
Whidden makes quality dies, I have several sets including forming dies, but the wait times can be long and expensive