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Thread: Bolt not locking back... need your help!

  1. #21
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    I have a hard time believing it's the pmags that are the problem as well, but I have an even harder time believing that two guns are suffering from the same problem when the only common denominator is the magazines. I guess when I try some other mags that'll help narrow down the issues.

  2. #22
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    I am not saying that PMAG's are the problem. What I am saying is that you need to ISOLATE the problem.

    It would help greatly if you had an AR that is absolutely known to be reliable.

    You then start with obvious things like magazines- the big thing is not buying some POS mags. Find some Colt mags or similar milspec aluminum mags and try them.

    If that solves the problem then you may be able to say it's a magazine issue. You then can test those suspected mags in the known performer AR and see what happens.

    If they work then the issue could be the lower. You have to have known quality stuff that works in order to rule out/ find the problem.

    Quote Originally Posted by SpyderMan2k4 View Post
    I have a hard time believing it's the pmags that are the problem as well, but I have an even harder time believing that two guns are suffering from the same problem when the only common denominator is the magazines. I guess when I try some other mags that'll help narrow down the issues.



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  3. #23
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    Were these 20 or 30 round Pmags?

  4. #24
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    Quote Originally Posted by SpyderMan2k4 View Post
    I have a hard time believing it's the pmags that are the problem as well, but I have an even harder time believing that two guns are suffering from the same problem when the only common denominator is the magazines. I guess when I try some other mags that'll help narrow down the issues.
    As Iraqgunz suggested, just don't get any aluminum mags available. You need quality mags to make a fair and accurate comparison. OKAY, NHMTG are excellent USGI mags, Bravocompany Mags (D&H) with the Magpul followers, as well as DSA mags, also with Magpul followers. You can get 10 of them for 89 bucks. http://dsgarms.com/ProductInfo/MA-02DSGG10.aspx
    For God and the soldier we adore, In time of danger, not before! The danger passed, and all things righted, God is forgotten and the soldier slighted." - Rudyard Kipling

  5. #25
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    Start with the least expensive fix and try your rifle:
    1-Try a known good quality bolt carrier. If your rifle starts running, you know the gas key is not sealed anymore,,,time to replace the gas key and stake it in place.
    next-if #1 didn't help
    2-Try a replacement gas tube with your original bolt carrier. The old tube may have a build up of residue from the 22 conversion that has not been blown clear by shooting .223. The old tube may have been twisted or damaged somehow to become slightly misalligned and not allow enough gas flow.
    next-if #1 or #2 didn't work
    3-The old standby, check your bolt gas rings. They my be worn down and leaking. Replace them with a brand new set. Test your set up again.

    Wild hunch and remote possibility,,,if the upper receiver is slightly out of spec, receiver that was mismachined and not allowing the magazine (feelips bottoming out too soon) to sit tall enough to function right....maybe it was ok for a while before being broken in and now caused trouble?

    I am leaning towards the gas leakage being the trouble....gas key, gas tube, bolt rings or a combination of all.

  6. #26
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    Quote Originally Posted by Iraqgunz View Post
    I am not saying that PMAG's are the problem. What I am saying is that you need to ISOLATE the problem.

    It would help greatly if you had an AR that is absolutely known to be reliable.

    You then start with obvious things like magazines- the big thing is not buying some POS mags. Find some Colt mags or similar milspec aluminum mags and try them.

    If that solves the problem then you may be able to say it's a magazine issue. You then can test those suspected mags in the known performer AR and see what happens.

    If they work then the issue could be the lower. You have to have known quality stuff that works in order to rule out/ find the problem.
    You got it. That's mostly what I meant... trying to isolate the problem. Part of the issue is that my friend JUST built his rifle, so he has fewer rounds through than I do, so it's certainly not "proven," but hopefully having good quality stuff on his that's still having the same issues will help narrow down the issue.

    Quote Originally Posted by rljatl View Post
    Were these 20 or 30 round Pmags?

    Both

    Quote Originally Posted by RogerinTPA View Post
    As Iraqgunz suggested, just don't get any aluminum mags available. You need quality mags to make a fair and accurate comparison. OKAY, NHMTG are excellent USGI mags, Bravocompany Mags (D&H) with the Magpul followers, as well as DSA mags, also with Magpul followers. You can get 10 of them for 89 bucks. http://dsgarms.com/ProductInfo/MA-02DSGG10.aspx
    That's the plan. Another friend has quite a few M16 USGI mags he got from the Army and are known to run well. I will be borrowing those.

    Quote Originally Posted by a308garand View Post
    Start with the least expensive fix and try your rifle:
    1-Try a known good quality bolt carrier. If your rifle starts running, you know the gas key is not sealed anymore,,,time to replace the gas key and stake it in place.
    next-if #1 didn't help
    2-Try a replacement gas tube with your original bolt carrier. The old tube may have a build up of residue from the 22 conversion that has not been blown clear by shooting .223. The old tube may have been twisted or damaged somehow to become slightly misalligned and not allow enough gas flow.
    next-if #1 or #2 didn't work
    3-The old standby, check your bolt gas rings. They my be worn down and leaking. Replace them with a brand new set. Test your set up again.

    Wild hunch and remote possibility,,,if the upper receiver is slightly out of spec, receiver that was mismachined and not allowing the magazine (feelips bottoming out too soon) to sit tall enough to function right....maybe it was ok for a while before being broken in and now caused trouble?

    I am leaning towards the gas leakage being the trouble....gas key, gas tube, bolt rings or a combination of all.
    That was pretty much what I've been doing... except instead of buying new parts, I'm borrowing them. Again, my friends BCM complete upper isn't locking back on them either. Neither complete gun locks back. His upper doesn't lock on my lower, and my upper doesn't lock back on his lower.
    Last edited by SpyderMan2k4; 09-29-10 at 23:09.

  7. #27
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    spdldr

    Often small gun springs are excessively strong. They can vary from batch to batch and manufacturers tend to try to err on the strong side for various reasons.

    Compare the "feel" of the resistance to actuation of your bolt catch to that of someone else's that functions well. If the spring is too strong it will resist the mag follower pressure just long enough so that the bolt head will pass over the catch before it has had time to rise to engagement height. If the spring seems stronger than a functioning one it may be necessary to replace it or clip off a couple of coils.

    Dave

    Boonie Packer

  8. #28
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    This was actually one of my first thoughts, as the bolt catch did feel really stiff. I clipped a coil off and it seemed the follower could activate the bolt catch a lot easier, but it didn't fix the problem.

    After poking around various threads, I came across some threads about the brass ejection chart. While obviously there's WAY more that goes into that chart than just how a gun is gassed, I did find it interesting. When I first got my AR (when I had no issues with it locking back), brass was ejecting at 3-4:00. I did find it kind of odd last week (when I noticed lock back problems), my brass was landing about 1:30. This COULD be an indicator of a previously mentioned idea, that my gun is overgassed (midlength upper with m16 carrier, and a standard buffer).

  9. #29
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    Out of curiousity did you ever call CMMG as I recommended and ask them what size their ports are?

    If you have a chance, why don't you humor me? Remove the gas tube and soak it overnight in some type of carbon cutter/ remover. Then reinstall it with a new roll pin.

    Hell- send your address to me and I'll send you a few for free.

    Quote Originally Posted by SpyderMan2k4 View Post
    This was actually one of my first thoughts, as the bolt catch did feel really stiff. I clipped a coil off and it seemed the follower could activate the bolt catch a lot easier, but it didn't fix the problem.

    After poking around various threads, I came across some threads about the brass ejection chart. While obviously there's WAY more that goes into that chart than just how a gun is gassed, I did find it interesting. When I first got my AR (when I had no issues with it locking back), brass was ejecting at 3-4:00. I did find it kind of odd last week (when I noticed lock back problems), my brass was landing about 1:30. This COULD be an indicator of a previously mentioned idea, that my gun is overgassed (midlength upper with m16 carrier, and a standard buffer).



    Owner/Instructor at Semper Paratus Arms

    Facebook: https://www.facebook.com/SemperParatusArms/

    Semper Paratus Arms AR15 Armorer Course http://www.semperparatusarms.com/cou...-registration/

    M4C Misc. Training and Course Announcements- http://www.m4carbine.net/forumdisplay.php?f=141

    Master Armorer/R&D at SIONICS Weapon Systems- http://sionicsweaponsystems.com

  10. #30
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    I have not called CMMG yet, mostly because I haven't even narrowed it down to my upper considering the BCM does the same thing.

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