Dimples on receiver and bolt

[jmoore]

A Rockwell "C" series hardness test uses a well defined angled punch that is preloaded and then loaded again to a specific force, leaving a very small indentation, the depth of which is measured by the machine using the punch shaft displacement into the metal before it's removed from the machine. (There's some older methods that measure the dimple by other means, but they wouldn't apply here, either.) Regardless, a Rockwell dimple is VERY small and regularly shaped, not at all like whats found on bolts, etc.

The hardness test would also not be accurate except on surfaces that are solid from the indentation site to the bottom of the test piece. You want no holes in the area! Some areas on a bolt lug would be OK as they're solid. But a bolt body has at least the firing pin hole bored through it, so that area is no good.

(BTW, I'd estimate a Rockwell punch mark to be maybe 0.010 0.015" max. in diameter on normal action parts. So small it's useless for an inspection marking.)