MC I was under the impression the subject of this posting is British Case Colouring! People may be trying to duplicate American case colours on your side of the pond so why the hell do they put them on English guns surely gunsmiths can have more than one methodology ? English action hardness has never been an issue as far as I can recollect and back to the AA Brown Video warping was also not an issue. So as I said there is something more in the process than heat Charcoal bone and water that at first look is simple but if you look deeper you will see that there is more in colour hardening than at first site.
