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Question on bluing stainless steel

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  • Question on bluing stainless steel

    I am going to blue my M40a1 that has a Hart stainless steel barrel on it. I also have an M40a3 with a Schneider barrel on it that is next on the list. I know that the spec for these is black oxide and that you cant blue SS in regular bluing salts. Is there a difference in a black oxide coating and regular blue. For both of these projects I will use Oxynate 84 since that is what I have. My question is will Oxynate 84 hurt the barrel at all? I will also plug the barrel to protect the rifling in it. I have emailed Hart about this but they dont blue their barrels at all so they were not any help. If you guys that have blued stainless steel barrels give me and help with this is greatly appreciated.

    Thanks in advance,

  • #2
    Oxynate 84 is what I used on my first build, and it has held up very well. The key is prep. Bead blast and hydrochloric etch right before bluing. Plug the bore before bead blasting so you don't mess up the bore. A warm etch might cause the plugs to pop. Some say it doesn't matter, but I made a plug using all thread rod through the bore, and rubber plugs compressed with a nut and washer at both ends. It worked fine. I would remove the plugs for bluing, but maybe that's not advisable? What you don't want is outgassing streaks, or hydrochloric acid screwing up your bluing bath. As far as I'm concerned, hot blue is a form of black oxide.
    You can take a Marine out of the Corps, but you can't take the Corps out of a Marine.


    • #3
      What does the hydrochloric etch do? Ive blued several other guns in regular blue but I haven't heard of doing that


      • #4
        For one thing, while glass beading cleans and roughens the surface mechanically, it only puts a texture on the surface dependent on the size of the individual glass beads, and the surfaces of the individual "craters" are hardened by the impacts of the beads that created them. An acid etch etches the surface on a molecular level, and attacks the hardened surface. Hot blue/BO takes and adheres much more easily on a surface that has been etched.

        The other reason why the blue takes better on an acid etched surface is because the acid activates the surface, really a necessary preparatory step to properly blue/BO stainless steel. Etching should be done immediately preceding the blue/BO, as the surface will passivate the longer it is exposed to oxygen between steps.

        I'm sure there have been many advances in the metal finishing industry since I was active in it, so you should consult with someone more up to date with current practices. Brownell's should have instructions available for their Oxynate 84 process, including surface preparation.
        Last edited by SemperFi; 06-22-2018, 12:56 AM.
        You can take a Marine out of the Corps, but you can't take the Corps out of a Marine.