AR Build - 1st shot problem

Discussion in 'AR-15 Discussion' started by TekGreg, May 27, 2013.

  1. TekGreg

    TekGreg Lifetime Supporting Member Lifetime Supporter

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    I built a new AR using a PSA lower, PSA LPK, and an upper custom built by a friend who is a Class III manufacturer. It has a chromed bolt of unknown origin, but appears extremely high quality.

    After assembly, I tend to run the gun a little on the wet side of normal for the first few hundred rounds to make sure nothing is damaged getting broken in. However, for the first time in several builds, this gun fired one round, unlocked out of battery, but the bolt only recoiled a very minor amount, maybe a quarter of an inch. A few taps with a punch and gunsmithing hammer backed the bolt out and extracted the round. Inspection shows nothing broken or galled, so I'm not sure what happened. Has anyone else experienced a condition like this before? If so, what did you do? I know a gunsmith should inspect it but I wanted to find out the cause first, if possible.
     
  2. Quentin

    Quentin New Member

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    Does the BCG cycle smoothly by hand? If excessive friction isn't noticed, and assuming good ammo, then maybe a gas leak...

    How did the brass and primer look?
     
    Last edited: May 27, 2013

  3. SSGN_Doc

    SSGN_Doc Well-Known Member

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    Yes, had a similar problem when a bolt on gas block was installed all the way up against the ridge on the barrel, aft of the block. It partly blocked the gas port, causing a under gassing problem, resulting in short stroking.

    Also saw it on a rifle, where the gas tube retaining pin walked out and the gas tube was floating, causing the gas port to get blocked.
     
  4. HockaLouis

    HockaLouis New Member

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    Not a "gas" issue if he had to use a hammer and punch to get the BCG back, right? I'd focus on the BCG, surrounding parts, and receiver.
     
  5. RRoss

    RRoss New Member Supporter

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    I would check the inside of the upper and see where the BCG was rubbing. if you have ANY damage to the upper I would get the gun to a smith asap. It could be something as simple as lubing the wrong areas or something as bad as the BCG being out of spec in its machining.
     
  6. CGS

    CGS New Member

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    Try a different BCG in your rifle and see what happens if indeed the bcg was truly stuck. Alternatively you may try your new bcg in another AR. That'll tell you if the upper or BCG are out of spec. Somestimes there is such a thing as tolerance stack. One part +.002, one part -.002 give you a .004 difference. Doesn't seem like alot, but enough to cause failure.

    If the new BCG causes problems something may be wrong with your upper receiver. The reason it's probably not a gas issue is because you had to tap back your bcg. Does the bcg move freely with the charging handle? You may still want to check the gas system. I usually do this by plugging the barrel extension with some cotton and blowing in the barrel. I do this while the gas block is loose and wiggle the gas block listen for differences in the pitch and tone of the whiste of the blown air.
     
  7. TekGreg

    TekGreg Lifetime Supporting Member Lifetime Supporter

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    Primer and brass were normal, but it seemed like the brass was holding the bolt closed. After extracting case, bolt seemed to cycle fine.
     
  8. TekGreg

    TekGreg Lifetime Supporting Member Lifetime Supporter

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    Seemed that the brass was what was locking up because there wasn't any resistance with light blows, i.e. didn't have to break it free, but resistance seemed to be in the chamber.
     
  9. TekGreg

    TekGreg Lifetime Supporting Member Lifetime Supporter

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    CGS, I will try new BCG as I have a couple if M-16s that just arrived that will be a good choice. I love the idea of checking the gas block and tube so will try that, too.

    Upper receiver didn't have any rub mark or gouge and BCG moved freely with charging handle when brass was extracted. I am going to disassemble, re-inspect, re-lube and test fire. I'll post here as soon as I can get to the range.
     
  10. Jpyle

    Jpyle New Member

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    You said it was a custom built upper? Let your friend look it over, he will be the most familiar with it.
     
  11. RRoss

    RRoss New Member Supporter

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    It sounds like you had a shell case that caused the problem. Another test fire should answer the questions.
     
  12. CHLChris

    CHLChris New Member

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    I had some really annoying failures when I first built my rifle (there's a sticky on my build and its problems in the AR-15 forum). After testing all sorts of things, it turned out to be the crappy Remington UMC ammo.

    I'm not saying this is an ammo problem, but most problems are mags and ammo.

    If this is a chamber problem--and that's what it sounds like--you really ought to have a gunsmith check out the headspacing. But you said the brass looked normal when it came out? Not bulging?
     
  13. fsted2a

    fsted2a Active Member

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    Just for sh**s and giggles, I would look at the gas key. Seems like the only plausable thing no one else has suggested. Except for gas tube alignment, and a reputable builder should have at least taken care of that.