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Thread: What's causing my case head burrs?

  1. #1
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    What's causing my case head burrs?

    I have a mutt M4 type carbine that I built. It has Stag upper & lower receivers, a Stag buttstock, a Double Star LPK, a Bushmaster bolt and carrier, an unknown charging handle, a Stag carry handle, and a Sabre 14.5" M4 type barrel with a permanently attached extended A2 type flash hider. Here's a picture:

    It has been 100% reliable so far, handles well, and is more accurate than I am. I do have something interesting happening though. The spent cases only eject about a yard or less. They don't get flung out like happens with my other AR's. Many of the case heads are also left with a bright smear mark and a sharp burr.

    It almost seems like something is slipping and then catching. I reload, so I'm going to have to file these burrs off. This has happened with both Prvi 55gr FMJ and Remington 55gr FMJ. Is this a sign of some sort of problem? Is there something that I need to fix?

  2. #2
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    My Sabre does the same thing, so does the Colt 6601 I shoot.

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    Top mark is the ejector, bottom mark is extractor.

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    Looks like high pressure signs.

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    Quote Originally Posted by Heavy Metal View Post
    Looks like high pressure signs.
    Primers look fine to me. Looks like the norm for 5.56 pressure case-heads from what I have seen.

    Anyone else have an opinion? I have several rifles which spit out cases like this, couple of Colt's and a Sabre Defence.

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    Quote Originally Posted by Hootiewho View Post
    Top mark is the ejector, bottom mark is extractor.
    This is common with ARs.
    The burr in the middle of the ejector "smear" is a little concerning.
    I would be suspicious of soft brass, or you may have a sharp ejector (or both).
    I would push some high quality M193 or M855 through it after a thorough cleaning of the bolt, chamber, and bore.
    Check the ejector for brass shavings.
    Jack Leuba
    Director, Military and Government Sales
    Knight's Armament Company
    jleuba@knightarmco.com

  7. #7
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    Thanks for the info guys. Failure2Stop, I think you may have a good point. I examined the cases more closely. While the Remington and Prvi both have the bright smear marks, only the Prvi actually has the burrs. Perhaps it's just a difference in the brass that causes them. It's nothing a file won't fix.

  8. #8
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    I get those too sometimes and I lay a piece of the sanding type paper, black with holes in it, the type used for drywall sanding on the top of my metal bench and give it a quick swipe after cleaning but before sizing. If you have a few thousands of burr on the case head you could end up over sizing by that much since the shell plate or holder is basically your zero point.

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    my CMMG M4 does the same thing with 5.56 pressure loads, but not with .223 loads.

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    I remove the ejectors from my bolts, and using emory cloth and CLP, I slightly radius the edge of the ejector. This small modification takes minutes, and helps to reduce the build-up of small brass particles that typically collect on the face of the bolt.

    I can get some pics up this evening if anyone is interested.
    “A leader is best when people barely know he exists, when his work is done, his aim fulfilled, they will say: we did it ourselves.” -Lao Tzu


    http://quibphotography.com/

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