MkI Bipod - plum colored mounting ring

[Mk VII]

It usually means the bluing salts bath wasn't hot enough, or was contaminated.

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[browningautorifle]

It usually means the bluing salts bath wasn't hot enough, or was contaminated.

They didn't seem to believe me...

[Bruce_in_Oz]

Heat-treated alloy steels are prone to this "purple" caper..

Something to do with the surface crystal structure. The "purple / crimson"' is a"ceramic" skin; hard and with a structure that , like traditional "blue / brown", holds oil to prevent corrosion.

If you GENTLY grit-blast the offending colour away and re-blue (proper hot-bath or slow steam chamber, it will turn a nice "matte" black.

You see components of various "Eastern Bloc" firearms that sport this colouration. It does the job. These are tools of the "trade", NOT "fashion models.".