I cut the hammer face back, drill a mounting hole along with a cross pin hole (to capture the not yet made "firing plate"). Then, I make a " firing pin " with a large front section to at least cover the area needed to strike the pin in the conversion ring (of either Howell or Kirst). After fitting, I harden the new "firing plate" , polish and fire blue it (just to be fancy!!).
I mount it in the hammer and "capture" the cross pin (upset material on both sides of the hammer) just like I do for the hammer roll pin .
That's how I fix that problem.
As some folks know, mine are dedicated cartridge guns so the hammers come to rest on the frame rather than the back of the cylinder (Howell) or the conversion ring (Kirst). That allows the full force of the hammer to contact the firing pin in either conversion and then the frame rather than beating on the conversion cyl itself.
Mike