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Firing pin cratering bushmaster bar-10

Mr. Friendly
Noticed I have some cratering around the firing pin on my bolt face. I was looking at some of my fired cases and noticed the primer was a bit mangled on one side. This rifle has had about 2,000 rounds through it, all winchester nato spec, no reloads.

Could some of the more experienced on here share their insight on the causes of this issue? The rifle still performs beautfully, and is one of the most accurate rifles I have ever seen with the nato ammo. Thanks for your help
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3 comments

Date Votes
  • Mobuck
    A slightly undersize firing pin will show cratering. It is also possible the dynamics of the rifle are causing some firing pin retraction after the primer has ignited. As long as there is no evidence of piercing, I would let it be and check for any increase in the amount of cratering.
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  • nononsense
    Todesengel,

    It might sound picky but the terms used need a little correction.

    This is a photograph of a 'cratered' primer.

    primercrateredye5.jpg

    This is a result of either a smaller diameter firing pin or more likely a larger diameter firing pin hole in the bolt face.

    This is the ring created by gas cutting erosion on the bolt face.

    boltfacegascuttingerosibj8.jpg

    The ring is formed by the primer leaking the hot plasma gas around its perimeter. These gases impinge on the bolt face and cause erosion.

    The cratering is stopped by bushing the bolt face or if the firing pin is smaller, replacing it with the proper firing pin.

    Leaking primers are caused by over pressure and/or enlarged primer pockets from previous over pressure excursions.

    Have a gunsmith check it over.

    Best.
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  • nononsense
    Todesengel,

    Good Catch! That'll certainly do it.

    I'm glad you took pictures, it really helps.

    boltar15lmtenhancedboltud6.jpg

    Best.
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