When carbon rich materials (in our case Wood/Bone charcoal) are heated, they begin to off gas carbon in the form of carbon monoxide and carbon dioxide. When steel is heated, it will absorb this carbon. Steel will begin to absorb carbon well below its critical temps, and can be hardened when quenched below its critical temp.
Mike...
There are just so many people in this hobby that just don't understand this, of course all of them have never actually hardened a piece of steel........they probably never will and love to argue numbers and inject negatives....with a firm belief that we are somehow structurally weakening old gun receivers......and making them brittle, the most common phrase you hear from the uninformed.....
I don't think I have ever heard of an action that failed from bone/charcoal "re-casing"--(not counting the 'El Torcho method')--, there may be some out there done poorly and over heated that failed, I am just not aware of any in my travels......
as long as the temperatures are kept within the envelope, the risk is held to a minimum IMO....
So, from a safty standpoint......there are many, many more shotgun barrel failures that are the result of grinding out the chambers and forcing cones and bores by the "barrel butchers" who actually remove lots of metal in different places.........IMO........
CZ...
"Well, what about the action that was repeatedly heat treated"...?....."It would take hours and hours to add a slight increase in depth from the prior state"..........
Very correct......at the temperatures we operate I think it would take quite a few re-casings before the molecular anatomy of an old gun receiver was destroyed.....and as you previously mentioned...most guns receive 'maybe one' re-case in their entire lifetime......
Best,
