HK went to coating all the internal parts in their black "HE" (hostile environment) finish several years ago due to stupid customers who were dropping their pistols in solvent tanks for lazy maintenance and then not re-lubricating them afterwards. In humid environments, this lead to the internals rusting. So instead of attempting to educate on proper weapons maintenance, they went to coating all the parts.
"Hostile Environment" is marketing. It doesn't tell me what it actually is, and I see no reason they couldn't be applying that brand name to several different products, the same way AT&T tries to call DSL and cable both "Uverse."
My understanding is that the slide and barrel are FNC with black oxide on top to make it nice and black. FNC involves enough (time * temperature) that it generally needs to be included in the engineering of the materials used for the parts from the beginning, as it will affect heat treat of steel.
The finish that can peel/flake/wear off extractors and slide lock levers, leaving the heat treated plum/orange/bronze steel underneath, seems to be something different.
It would seem to be a remarkable measure to me if the MIM action parts got re-engineered to work when FNC'ed. Seems more likely that we're now seeing some kind of coating similar to the levers and extractors. Any idea what kind of coating it actually is?
Any idea when the change was made?
Any idea how one might strip it to bare steel? (Would like to avoid grit blasting anything.)
FWIW, I'm mostly interested in the hammer axle and hammer.