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Look at the roots of case-hardening...…..
In antiquity, case-hardening had to be used to ensure the metals used at the time could withstand the pressures of the ammunition used at that time.
Shortly afterward, the resultant colors became a selling feature.
Today,
MUCH better/harder modern steels are used which, when hardened, didn't display the same coloring that used to occur, so most manufacturers did some things that made their product marketable.
They polished the hardened metal to a bright or satin (aka: French Grey) and/or colored the steel blue/black by various methods.
IMO, modern guns that receiver true case-hardening colors are usually applied to the upper end of the various maker's product lines (some makers make only high-end products).
Generally, since manufacturers that market products in the US must follow US federal Law:
https://www.ftc.gov/news-events/media-r ... dvertising
The federal Law demands truth in advertising, so anyone seeking a particular product (like true case-hardening) should determine that the correct terms are used to describe the finish.
(Some makers use ambiguous terms in product description that can be interpreted differently, but still pass the legal test)
IOW, caveat emptor...……
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