Lets play guess the diameter...

Discussion in 'Main Message Board' started by carlsbad, Nov 12, 2019.

  1. Bc'z

    Bc'z Gold $$ Contributor

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    Its pictured above .086
     
  2. carlsbad

    carlsbad Lions don't lose sleep over the opinions of sheep. Gold $$ Contributor

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    Thanks BC'z. Sorry that wasn't clear.

    This firing pin as found was .078 diameter in a .086 hole. I'm sure the guy was having some cratering. There was some damage to the end of the pin, probably from the brass pinching between the pin and the wall of the hole. The issues machined off. Pin is now .059. Hole is .060. I'll post photos of the "as left" later or tomorrow. --Jerry
     
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  3. msinc

    msinc

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    No sir, it was very clear and I saw it before I posted. My point is that it doesn't matter what , to the thousandths, it actually measures...it's waaaaaayyyyyyyy too big!!!!
     
  4. carlsbad

    carlsbad Lions don't lose sleep over the opinions of sheep. Gold $$ Contributor

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    OK. msinc. I see your point and you've mostly answered the bonus question. The fit is not nearly as important as the diameter. Once the brass starts extruding/cratering it can push the firing pin up. With a 50,000 cartridge pressure, the force pushing the primer brass through a .086" hole is 290 lbs. It can push the fring pin back into the hole since that is much stronger than the spring.

    Now a good firing pin fit is better for a couple of reasons:

    1. Keep dirt etc out.
    2. The firing pin hole is the key for cratering/piercing but for durability, the firing pin should be as large as possible and still fit i the hole. I don't like to go below .058 for firing pin diameter so the tightest fit gets me the tightest hole.
    3. If you do get cratering, which is very unlikely with a ,060 hole, the tight fit will prevent brass getting pinched in the gap.

    --Jerry
     
  5. Bc'z

    Bc'z Gold $$ Contributor

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    Does this also apply if the rifle will never see srp brass?
     
  6. carlsbad

    carlsbad Lions don't lose sleep over the opinions of sheep. Gold $$ Contributor

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    Yes, SRP vs LRP is very little difference. LRP is slightly thicker and you can get buy sometimes when your situation is borderline. But I'm bushing more bolts for guys shooting LRP brass now than SRP. --Jerry
     
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  7. carlsbad

    carlsbad Lions don't lose sleep over the opinions of sheep. Gold $$ Contributor

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    Finally got around to uploading the after pic. 20191114_222159.jpg
     
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  8. Bc'z

    Bc'z Gold $$ Contributor

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    Good to know I now have a plan.
    I can't wait!
     
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  9. dogdude

    dogdude Egan O'Brien Gold $$ Contributor

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    Jerry has done 1 large, 1 small, with another large on the way, both look like what is posted in #47 :)
    The first small I sent (Bat) was piercing badly, when it came back, I took the same ammo that was piercing and the primers looked Perfect :D @carlsbad is Da Man
     
  10. snert

    snert Silver $$ Contributor

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    The fit is not nearly as important as the diameter.

    Thats what she said...
     
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  11. jimmymac

    jimmymac Gold $$ Contributor

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    ...and if you’ve ever heard those words she was just trying to make you feel better about your shortcomings. :D
     
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