Help with AR-15 BCG

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  • dbledoc

    Ultimate Member
    MDS Supporter
    Apr 8, 2013
    1,528
    Howard County
    I have NiB BCG that I am having a heck of time trouble shooting.

    If I load a single round in the magazine, it functions fine. The empty case is ejected and the bolt is held open. The empty cases are ejected consistently in the same area about 5 to 6 feet to my right and behind me a foot or 2.

    If I load more than one round in the magazine, the empty case does not eject and the next round is gets jammed up under the empty case. I have tried a number of different magazines (Pmag, Lancer, Troy, ASC) and the same problem happens.

    So, I tried the BCG in a rifle which normally functions fine and the same problem occurs. I took a different BCG and put it in the original rifle, and it works fine. So I am convinced the BCG is the problem. FYI, I lubed the BCG using the method described by Lord Chad.

    If I load a magazine and cycle it by hand, the rounds eject fine and it strips the next round into the chamber fine. I tested the BCG by standing it up on the bolt face and it passed the gas ring test. I used the reverse torque test on the gas key screws and it failed, so I changed the gas key screws and torqued them to around 55 ft-pounds. Same problem....So I am at a loss as to what to do next. Any help/advice is much appreciated.
     

    outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    50,026
    You may have too much bolt speed. I'll step aside for the true experts at this point.
     

    BradMacc82

    Ultimate Member
    Industry Partner
    Aug 17, 2011
    26,177
    Bolt's cycling too fast, aka - over-gassed rifle. I take it that you have a carbine-length gas system?
     

    dbledoc

    Ultimate Member
    MDS Supporter
    Apr 8, 2013
    1,528
    Howard County
    Just for the sake of trying an easy fix... Have you tried firing your rifle with an H2 or H3 buffer in place of the standard carbine buffer?

    Don't have the heavier buffers yet... this is a new BCG and have been to the range twice with it. Once when i discovered the issue and the second when I took alternative BCG to trouble shoot.
     

    smokey

    2A TEACHER
    Jan 31, 2008
    31,522
    Is there any odd wear in the upper/ buffer tube? If you hand cycle two rounds through, does the second have any odd marks from the bolt carrier? Most phones/cameras now do slow-mo video recording, may be interesting to grab a video of the gun cycling in single feed/mag feed next time u go shooting.
     

    outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    50,026
    Sorry, I misread. Disregard my previous post.

    So did I!:o Could be a gas key issue?

    If you go the heavy buffer rout, just buy an H-3 and add one tungsten weight at a time from it. Though I now doubt it is your problem?
     

    pwoolford

    AR15's make me :-)
    Jan 3, 2012
    4,186
    White Marsh
    I had a NiB BCG that did that before...I ended up exchanging it for a new one. I tried new gas rings first and it didn't help.
     

    clandestine

    AR-15 Savant
    Oct 13, 2008
    37,031
    Elkton, MD
    The Gas Key can still leak if the deck is warped where they seal.

    If the Gas Key Bore is too large it will also leak gas. A bad gas seal can allow it to run with no rounds adding friction on the bolt carrier, but will cause issues once friction happens. If you want to gauge the gas Key, but a Pin Gauge from MSC, they are like $4.00. A .182 is a FAIL, .180 is a GO.

    I have seen way too many problems with NiB stuff, it drives me nuts.

    Its also possible that its somehow overgassed and causing rounds to pop out of the mag then the carrier bottom out in the rearward stroke. Remove 2 gas rings to test.
     

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