Serious problems that can occur during the case hardening process namely distortion and cracks. For example in my early life [50 plus years ago] I was considering recase hardening a gun of mine.To this end,I visited a well established Birmingham gunmaker and asked for a quote for recase hardening the action.The reply from the owner was;"only if you accept full responsibility for any distortion or cracks that may develope during the hardening process." Then to reinforce his position,he went back to the workshop and returned with the actions of a pair of Boss sidelocks that had been recase hardened.One action appeared sound the other had cracked during hardening.
Case hardening of parts such as the action of a shotgun that have many variations in section thickness and have sharp corners present, pose a significant challenge.The packing of the parts in the hardening box,protection of thin sections to prevent their conversion into high carbon steel, temperature controls and quenching methods are all critical if cracks and distortion are to be avoided.
For the above reasons I have avoid guns that have been re hardened.
