Here is an email from Jack (an SEI employee) to Anthony from Croc's Gun Shop. It is pretty enlightening to see this one of many industry standards that SEI has started.
I was able to get some pictures done and edited for you to send out in your newsletter.
These are the cross sections of our receiver parts mounted in epoxy. These are samples that were done form last year’s batch. These mounts check the accuracy of our case depth and core hardness. There is no industry SOP as to when or how often this should be done, it is determined by Ron. Since perfecting the heat treatment process on his receivers in 1985, Ron has periodically sent out receivers from several different batches to get tested, just to assure that they have been staying within his heat treating guidelines. Ron doesn’t think that there is any other manufacturer out there that goes to the same lengths of quality control for their heat treatment. Material 8620 is very predictable in heat treat. The heat treat processes for the M14 in 1957 were far different than they are today, due in large to EPA restrictions. We have found that on de-milled M14 Receivers, that core hardness is as high as 45, which is extreme, with case depth as much as .0020. With today’s technology, it is much easier to control and predict the outcome of a heat treat on a given material than it was back then. We know that the USGI M14 Receiver when de-milled, were sometimes hit on the op-rod side middle with some type of hammer blow which broke them. The receiver would withstand a great deal of compression, but lateral strikes could not be tolerated very well.