Russ,
I'm no metallurgist, but you're on the right track now. My understanding is that all the vintage American actions are mild steel, of carbon content below which martensitic hardening is possible. This might be a .10 to .20 carbon content.
The exact temps and times for these processes seem to be somewhat protected by those that have learned the hard way by damaging/warping recievers.
I recall asking Oscar about casehardening a modern reciever that is a martensitic alloy. He didn't know, or wouldn't take on, coloring a modern medium carbon alloy reciever. He emphatically recommended Doug Turnbull for such work. As I understand it, the trick is to ensure proper hardening processing for such steels and still get colors. He warned not to trust just anyone that does casehardening to this job. A thorough understanding of martensitic hardening and tempering processing is needed.
