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Thread: Bolt not locking to rear

  1. #1
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    Bolt not locking to rear

    This is the second time my gun has done this.

    When I shoot the last round in a mag, the bolt doesn't lock to the rear. This happened a few months back and I sent it back to the manufacturer for repair. I bought from a local place (didn't read this forum at the time) and they had it "fixed" in a couple days. They told me it has to do with the amount of gas coming back from the gas port.

    Is this A: A normal problem, B: Something that can be fixed forever by tuning the gas port to a certain point, C: Something I can fix myself?

    I have no gunsmithing experience.

    Thanks for the help.

  2. #2
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    Did this shop explain exactly what they did to correct the short stroking the first time? I would look there for starters. After-market gas block slipping perhaps?
    “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


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  3. #3
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    Embarrassed to say it, but I didn't even ask. They were so highly recommended that I just assumed it wouldn't happen again. I realize now how foolish that assumption was.

  4. #4
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    Successful tips for solving problem.

    1. What is the make and model of the weapon?

    2. What type of buffer and spring do you have?

    3. What type of ammo were you using?

    4. What type of magazines?



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  5. #5
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    Well the make is predator customs, not sure of the model. Its a local company from Knoxville. Its a 16 inch m4 style AR.

    Commercial tube, the spring is what was installed by them.

    Ammo was federal 100 round box from Walmart.

    PMAGS.

  6. #6
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    does it lock back when you charge the gun manually?

  7. #7
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    Quote Originally Posted by mnoe82 View Post
    Well the make is predator customs, not sure of the model. Its a local company from Knoxville. Its a 16 inch m4 style AR.

    Commercial tube, the spring is what was installed by them.

    Ammo was federal 100 round box from Walmart.

    PMAGS.
    what buffer (does it have an H or any other markings?)?

  8. #8
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    Yes it locks back manually.

    I'm at work right now. I don't know what markings are on the buffer yet but ill check when I get home.

    I'm assuming by the lack of immediate fix that this is an unusual problem? Anyone ever heard of adjusting the amount of gas coming back from the gas block or were they just feeding me a line?
    Last edited by mnoe82; 07-07-10 at 12:04.

  9. #9
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    Quote Originally Posted by mnoe82 View Post
    I'm assuming by the lack of immediate fix that this is an unusual problem?
    Short stroking is one of the more common AR problems. The difficulty is troubleshooting due to the variety of probable causes. Troubleshooting over the internet doesn’t make it any easier…LOL.

    Since you’ve had similar problems in the past with this weapon, and took it in for repairs where you were told the defect was in the gas system, now that the weapon is exhibiting similar symptoms, that is where I would personally start.

    But since we don’t know what corrective action the shop took, we are back to square one.

    - What type of gas block is on the weapon? If it is of the set-screw variety, could the block have shifted, partially blocking the barrels gas port?

    Going back through the gas system from there:

    - Is there gas leakage where the gas tube enters the FSB or gas block?
    - Is the gas tube worn, causing excessive clearance between the gas tube and carrier key?
    - Bolt carrier key loose?
    - Bolt gas rings worn?

    Another not too often occurrence would be excessive carbon build-up in the gas tube.

    ETA: These are of course a few probable causes on the gas system side. There could be a mechanical problem as well.

    A few of those probable causes might be:

    - Lack of lube.
    - Interior of the weapon excessively dirty or fouled.
    - Obstruction in the receiver extension limiting carrier movement during firing.
    Last edited by Quib; 07-07-10 at 13:29.
    “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


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  10. #10
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    Or weak magazine springs that are strong enough to lock the bolt back when you're doing it manually, but not strong(fast) enough to get up in time to lock it back when the BCG is going much faster.

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