The limiting factor on John's conversion is definitely being able to prevent crimp jumping on the bullets. Joohn has shot up to 240 grain cast bullets to over 1,700 fps, but these are single loaded. He's tlod me about some ammo being loaded in Florida that holds the crimp well, but I haven't gotten any yet. I would like to have a Keith in the 240 grain range for this revolver. I believe that at 1,000-1,200 fps, nothing we have in the lower 48 would hold it.
Elmer had similar problems with factory ammo in the fight with the bull elk.