New AR, Bolt wont close with round in Chamber

Discussion in 'AR Talk' started by basesohc, Apr 13, 2008.

  1. basesohc

    basesohc XDTalk Newbie

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    Just finished my first AR. I built the lower and purchased the complete upper. I first noticed that when I cycle the bolt, it would not close completely (just felt really tight). After a lot of cycling, it seemed to loosen up. I took it to the range today to put the first shots through it.

    When loading a round, the bolt will still not close. The forward assist does not help. When I pull on the charging handle to eject the round, it feels like something is physically wedged, as it takes both hands and a large grunt to eject the round. If I manually feed one round (no mag) and close the bolt, it closes completely about 8-9 out of 10 times. I was shooting some 5.56 bulk ammo I purchased. When I tried my buddies .223 ammo, it actually cycled through some. It still hung up, but not as often. The upper is a full LMT upper w/BCG and charging handle. I also swapped BCG's with my buddy and my bolt worked fine in his Bushmaster, his showed the same symptoms in mine.

    The ejected 5.56 rounds look like they are getting marked up by the barrel really good. Chrome lining a little thick? Something related to the BCG? Thanks for the help.
     
  2. nikon777

    nikon777 XDTalk 5K Member Founding Member

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    Interesting. I can only suspect you didn't put the lower together properly.
    Also, what kind of magazines are you using?
     
  3. basesohc

    basesohc XDTalk Newbie

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    I am thinking more of the bolt/barrel myself. I swapped complete lowers with my buddy and mine ran flawlessly with his upper. It seems to be the bolt/barrel combo where I see the problem. I am using new magpul pmags.
     
  4. nikon777

    nikon777 XDTalk 5K Member Founding Member

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    Out of spec chamber or something perhaps.
     
  5. forum

    forum XDTalk 100 Member

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    Is your barrel marked .223 specifically? if so the 5.56 probably wont function well, if at all in it.
     
  6. ARin

    ARin XDTalk 500 Member

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    lmt doesnt make 223 chambers.

    swap your upper onto a different lower also, and see if anything changes.

    if not, send the upper back to LMT.
     
  7. basesohc

    basesohc XDTalk Newbie

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    5.56 marked.
     
  8. f0cker

    f0cker XDTalk 100 Member

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    .223 and 5.56 chambers are the same dimensions internally, it's the strength difference. 5.56 rounds create a lot more pressure than .223 rounds.
     
  9. nikon777

    nikon777 XDTalk 5K Member Founding Member

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    Actually, there are slight dimensional differences between the two.
     
  10. ARin

    ARin XDTalk 500 Member

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    wrong wra wrong wrong wrong!

    dimensional differences.

    The AR15.com Ammo Oracle
     
  11. hardwarz

    hardwarz XDTalk 100 Member

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    Check for interface between the BCG and the gas tube.

    Hardwarz
     
  12. Ed Ely

    Ed Ely Super Moderator Staff Member Founding Member

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    Humm!! Guess I pulled up the wrong site -


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  13. ARin

    ARin XDTalk 500 Member

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    [​IMG]

    But like i mentioned before, its a non-issue, as LMT does not make any bbls with 223 chambering.
     
  14. snertley

    snertley XDTalk 100 Member

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    I would check your gas tube to make sure its not to long. The other question I have is did you have the head space checked? It is possible that it is not correct, even though you bought it as a complete upper.
    Good luck.
     
  15. CharlieHo

    CharlieHo XDTalk 500 Member

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    Sounds like a chamber issue to me. Give LMT a call to see how they want you to handle it
     

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