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Is This Primer Flow?

Discussion in 'Handloading and Reloading' started by otisrush, Apr 9, 2019.

  1. otisrush

    otisrush Member

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    This is range-scrounged brass. This wasn't loaded by me.

    Is this what "primer flow" is? I saw reference to this term in another post.

    I'm just trying to learn what is going on here and what is causing this. It was quite difficult to get a representative picture of this. You can kind of see it here - but there is a ridge/raised part beyond the actual firing pin strike. I'd normally think this means high pressure in general - but the edges of the primer itself look reasonable to my relatively-amateurish eyes.

    Thoughts?

    Thx.

    OR
    Primer.jpg
     
  2. ReloaderFred

    ReloaderFred Member

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    No, that's caused by an oversized firing pin hole in the bolt face.

    Primer flow is when the metal moves to the outside of the primer pocket and is noticeably flatter and larger than normal.

    Hope this helps.

    Fred
     
  3. <*(((><
    • Contributing Member

    <*(((>< Luke

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    When I think of primer flow it is when the primer has flattened out and fills the beveled edge of the primer cup on the cartridge. I wouldn't call that primer flow. I would call that an oversized firing pin hole.

    @ReloaderFred beat me to it.
     
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  4. otisrush

    otisrush Member

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    Thx guys.

    OR
     
  5. fxvr5

    fxvr5 Member

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    Looks like it was shot in a Beretta. Some guns leave a characteristic 'stamp' on the primer because of the firing pin hole design. Glocks have a rectangular firing pin hole and you can almost immediately identify if a round has been fired in a Glock.
     
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  6. 243winxb

    243winxb Member

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    [​IMG]

    Flow. May come from pressure or the type of bolt face.

    High pressure can make the primer flow around the firing pin, if there is excess clearance. Had this with CCI 400 primers at midrange loadings. Changing to Rem 7 1/2 primers cured it.
     
    Last edited: Apr 9, 2019
  7. Toprudder

    Toprudder Member

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    M&Ps leave a distinctive pattern around the firing pin as well.
     
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  8. ATLDave

    ATLDave Member

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    Yeah, my M&P puts sort of a teardrop shape around the firing pin mark.

    As for whether those kind of marks constitute "flow," I suppose it's literally true that the primer is flowing into the firing pin channel under pressure. So, yeah, it's "flow." But it's not the kind of flow that is a sign of overpressure.*

    *Note that relying on primer flow to detect pressure is a dicey business, especially since cartridges are designed to operate at significantly different pressures. A double-charged 38 special case might be 10k or 15k past SAAMI, yet still shy of 9mm +P pressures. How does the primer know whether it's being used in cartridges in an old Model 10 revolver or in 9mm cartridges in a CZ Shadow 2? It doesn't. It can't.
     
  9. otisrush

    otisrush Member

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    This is a REALLY good point that had never occurred to me: For a given brand & construction of primer, it takes a certain amount of pressure to flatten it out. What that pressure is is what that pressure is - and doesn't change whether it's being fired in one caliber vs another.

    Great clarification and reminder.

    Thx.
     
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  10. sparkyv

    sparkyv Member

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    I've heard this called "cratering".
     
  11. 243winxb

    243winxb Member

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  12. rfwobbly

    rfwobbly Member

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    BTW...
    Nice manicure. :D
     
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  13. otisrush

    otisrush Member

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    I do what I can. ROFL
     
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