RWTF;
All that is fine by me, & I was not arguing the virtues or lack thereof of the M12. I like doubles & could care less one way or the other. All I was saying was that I would bet my last dollar, just prior to coming off a 40 day fast (& I'm a big eater, incidently) that "IF" a M12 firing pin is case hardened it was not made of 4140, Or "IF" it was made of 4140 it would not have been case hardened. But hey, don't forget you're the one who named the metal, not me & what the receiver is made of has little bearing on the firing pin. The receiver of a M12 is not case hardened incidently, but blued.
