Maybe I'm doing the hardening wrong. When I have tried to harden either the punch or the die ,I got a lot of warping. the punch went out of round and the die( the bigger piece with the slot) warped down and mostly closed the slot .They were hard but useless. Now I try to use annealed bolts to make this stuff. Sometimes a useless rifle barrel is used. They are hard but, workable . One of my plain base dies ( a 9mm size) has made over 20,000 gas checks and no noticeable deterioration has happened.
n.h.schmidt