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Old August 14, 2012, 12:33 AM   #3
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Join Date: July 15, 2012
Location: Wonderful, Windy Wyoming
Posts: 133
I'll second what Dfariswheel has said. Bolts, and not just M1A/M14 bolts, are heat-treated to increase the yield strength of the bolt lugs and increase hardness to decrease deformation of the lugs under recoil.

But the M14 (later M1A) bolt was one of the most troublesome parts of the M14 design. There were several failures of the bolts in the late 50's, and the heat treatment of the bolt's steel underwent several revisions from 1960 clear up to 1992.

Typical of the heat treatment of the M14 bolt is that the surface case was 0.012 to 0.018 deep, and the surface hardness was in the 54 to 60 Rockwell C range, with the inner core being 33 to 42 Rockwell C. To accomplish this type of hardening treatment would require a furnace with a carburizing atmosphere, then a quench, then tempering to probably no more than the 425F to 450F level.

Translation: Even if you're quite skilled at heat treating steel, you're probably not going to replicate the mil-spec heat treatment of the bolt without some sacrificial bolts so that you can experiment to get the time period for the casing to achieve the correct depth of case.
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