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you do realize that quenching in oil after heating it to that point does make it harder, and more brittle ?? shold give about brinell 55 where as water would give approximately brinell 60 ..
 

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Discussion Starter · #6 ·
in a two pound loco, nope ...
but in a gun, yup ...
depends on end use, your's is okay ..
i am a 01 and 03 F.F.L. holder, i was a small arms repair instructor at Aberdeen proving grounds. this method is safe to use in ANY firearm. not a whole lot of stress on a side plate screw in a revolver or the grip screw in a 1911. there are not a lot of screws in ANY modern firearm. in the last 5 years i have broken ZERO of these black screws.
 

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well, in my opinion it should be tempered to reduce hardness ... for firearm use..

as far as qualifications i have been doing firearms repair for forty years, and am qualified to repair long rifles, restricted, and prohibited firearms .. including fully automatic machine rifles / pistols, i don't ship TO the us, just FROM .. mostly gun parts corp ..
but for loco use, it's perfectly fine as hard as it is..
 

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If you say so. In that case, I don't have many zinc plated screws, it's worked on every screw I've tried it on.

When I do a search, I see why it works for me.

Use ‘Gun Blue’ to Instantly Blacken Hardware

My favorite way to blacken steel, iron or even zinc-plated hardware is to brush on a thin coat of liquid “gun blue” – typically a combination of selenious acid, nitric acid and cupric sulfate. If you brush on a thin coat it will blacken a ferrous metal almost instantly, including zinc-plated hardware.
Obviously, it works for this guy as well.
 
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