It seems to me that a point of some significance is being overlooked. Whether or not some strength is added to the affected steel by the case hardening process is really not the point. Even if it is (or not) the film-like depth of the hardening contributes little and the OVERALL measurable fail point of the action as a whole is unlikely to be significantly, as in measurably, strengthened. And as best as I understand it the case coloring had no intended result of contributing to the strength of the action. Comparing case hardening (superficial) to heat treating (to the core) does not seem to me to be a tenable position.

JMO of course

Dr.WtS
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