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Heat treating a trunnion?

Discussion in 'Maintenance & Gunsmithing' started by KidJavelin, Jun 16, 2013.

  1. KidJavelin

    KidJavelin Puget Sound Member

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    I'm kicking around the idea of a home build using AR parts. The barrel/extension assembly will be standard fanfare, but I was thinking about pressing/pinning it into a 4140 trunnion, which in turn gets welded into a section of 4140 box tube.

    The question I have is that since I am planning on using the AR barrel extension, do I really need to have the trunnion heat treated? I imagine, just for safety sake the answer would be yes, but I thought I'd float the question.

    Oh, and does anyone know where I can get the steel parts heat treated at? Is it something I could do at home since they are fairly small parts?
     
  2. Mark W.

    Mark W. Silverton, OR Bronze Supporter Bronze Supporter

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    4140 spec sheet

    4140 Alloy Steel Data Sheet

    your nor going to get it very hard at all RC54 is less then a crappy Pakistani pocket knife would be heat treated to.
     
  3. KidJavelin

    KidJavelin Puget Sound Member

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    I thought that's what most builders use. Am I mistaken?
     
  4. Diamondback

    Diamondback A cold, wet green Hell Well-Known Member

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    IIRC ordnance-grade carbon-steel is usually 4340.

    But I'm not a metallurgist and I didn't stay at a Holiday Inn Express last night. LOL
     
  5. eganx

    eganx Kingston WA Active Member

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    If you use 4140 and have a proper heat treat you'll be fine. RC50 is adequate. Were not talking tool steel here.....although I have seen some milled chinese AK's harder than a honey-moon pecker

    If you heat treat post machining you will get some dimensional distortion
     
  6. KidJavelin

    KidJavelin Puget Sound Member

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    Thanks Eganx. I did a bunch of checking and a Rockwell C hardness of 54 is more than adequate for edged weapons, so I would think a trunnion with a similar hardness would be fine. I understand there will be some distortion after treating, but I'm thinking it's essentially just going to be a block of chromoly (I think that's what 4140 is normally referred to by other folks) with a hole that the extension gets pinned into, so it shouldn't pose too much of a problem.

    Oh Diamondback, 8620 steel is used in M1/M14 receivers because they are cast. It offers excellent pouring characteristics, is easily machined, and can be hardened to meet military durability needs. Just thought I'd let you know I found info on that as well, and I know nothing about a Holiday Inn.

    Eganx, I see you're in Kingston. I'm south of you in Port Orchard, do you know where I could get the heat treat done locally?
     
  7. eganx

    eganx Kingston WA Active Member

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    If you get with me.....I can get it heat treated for you....