Making firing pins

Discussion in 'Technical Questions & Information' started by LDBennett, Jul 19, 2009.

  1. LDBennett

    LDBennett Well-Known Member

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    I answered a question somewhere here or on Rimfire Central and I can not find the question or my response to modify it so I'll just make a general post to correct what I said earlier. I hope the right person gets the corrected answer.

    My thoughts were that you needed to make a firing pin out of drill rod. Apparently that is wrong according to the guru's at American Gunsmithing Institute (AGI). They say to make it out of mild steel and case harden it with Kasenit then anneal it back to mild steel hardness. This gives a hard exterior with a softer tough interior, a much better condition for a firing pin, according to them.

    If you need more details I can supply via PM a copy of their exact response.

    Sorry about the earlier mis-information. Sometimes experience trumps theory (??) or perceived theory, at least.


    LDBennett
  2. Bindernut

    Bindernut Well-Known Member

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    Yup, drill rod will work but it will be more brittle than a case-hardened mild steel one as suggested by those guys.

    I've only made a couple of short firing pins for old single-action shotguns and I turned both of them with a piece of Grade 5 bolt shank as the base stock, hardened and annealed afterwards. I know one of those pins is still going strong after about 10 years of amateur trap league shooting. I talked to the guy I made that pin for about a year ago, and the pin is holding up great with no deformation to it or the hammer.

    I would guess that a longer pin would really benefit from a mild/case-hardened pin.
  3. wabryan1

    wabryan1 New Member

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    One more question.
    I had a new firing pin made for me. I don't know what steel he used, but he didn't heat treat it. How do you "draw it back"?
  4. LDBennett

    LDBennett Well-Known Member

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    wabryan1:

    Steel can only be heat treated if it has some carbon in it. What is being done in heat treating is freezing the crystalline structure in one of several possible configurations. The structure that you get from heating it to red hot and cooling it rapidly is a harder structure then if the cooling is done very slowly (called annealing) and the crystalline structure is allowed to take its low temperature configuration. Its all about how the carbon molecules are placed in the crystalline structure.

    When we force cool red hot steel, we freeze its crystalline structure. To get to somewhere between full hard and full soft, we heat the full hard steel to an exact intermediate temperature and hold it for some exact period of time to allow the carbon atoms to partially rearrange themselves leaving less of the steel in its full hard state. That is called drawing the steel. You are drawing the hardness to some lower level of hardness. It is a science to get it just right.

    But according to AGI that is not the process to use for a firing pin. They say use mild steel (which CAN NOT take a heat treat), case harden it (allow carbon atoms to migrate into the surface layer of the mild steel making a hard case around the tough mild steel interior). Kasenit is a powder (probably pure carbon) that you put all over the surface of the part when it is red hot so it will infuse into the surface. That surface is then hard from the carbon and since mild steel will not harden with heat alone, the inside is still soft and tough. The "case" is only a few thousands of an inch thick but makes the part's surface more wear resistant and less like to peen over in the firing pin case.

    LDBennett
  5. Bindernut

    Bindernut Well-Known Member

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    Actually, you can harden and temper mild steel. It just has a fairly low carbon content so you won't be able to harden it as much as some of the better alloys that have higher carbon content...thus the AGI's suggestion to case harden it to achieve that outer shell. I've made lots of tools out of plain old rebar and mild steel stock...but never any gun parts.

    Bill Deshivs or one of the other knife guys that hang around here would be able to expound on the different steels better than I can.
    Last edited: Jul 22, 2009
  6. LDBennett

    LDBennett Well-Known Member

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    According to what I have read, iron has too much carbon and is very brittle (cast iron, for example). It is processed to wrought iron with no carbon. Steel is wrought iron with some small amount of carbon added and mild steel is the least amount of carbon added and still be called steel and not wrought iron. I think the carbon content for all steel goes from about .1% to 1%. AGI claims the mild steel will not take hardening to any measurable degree but with some carbon in it, it might be changed slightly by the process.

    AGI has a Video course on hardening and I have not yet bought it. In my engineering education some 45 years ago we studied Strength of Materials with a heavy emphasis on steels and their various crystalline states. Wish I could remember more of it. I have not seen the necessity to take a course of practical application when I rarely if ever need to harden anything, but I may buy the course anyway.

    LDBennett
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