My recollection from Mr Galazan's tour was that the receiver is made of 4140 (.40% carbon) and is martensitically hardened (thru hardened) prior to machining.
In a correspondence with Oscar Gaddy, he alluded to generating the case colors while still acheiving proper core hardness for a martensitic steel. He didn't provide details but suggested that if I had such a project, he'd recommend Doug Turnbull for the job. I don't recall him saying that the case colored martensitic steel gun would be actually case hardened or just properly thru hardened when done.
