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Thread: AR15 build problems

  1. #1
    Sniper MorrisWR's Avatar
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    AR15 build problems

    Finally got around to building my AR15 a few weeks ago and then finally had time to shoot it yesterday. It shot well 90% of the time but a few times I had two issues. On a few rounds it did not fire and failed to extract when I manually pulled back the bolt. It appeared like light strikes on the primers with those rounds but the fired rounds looked good. Bolt not catching round correctly perhaps? The other issue is sometimes the bolt did not lock back after the last round was fired.

    I ran different magazines and both 5.56/223 but did not notice a consistent change with either ammo type or mags.

    It is a CMMG 16" barrel with mid length tube, generic forged upper and bolt carrier group (11.1 oz), BCM stock kit (standard carbine buffer @ 2.9oz, 11.5" spring). Spikes lower kit and receiver.

    I am fairly certain the gas block/tube is aligned properly because I measured it and screw aligned with indent in barrel. I was thinking it might be a bolt issue or buffer/spring and have some parts from my sons Colt 6920 I can test it with next time I am out. I thought I would first try swapping bolts (Colt is 11.5 oz) and then buffer/spring changes. Colt buffer/springs are 10.5" and an H buffer; it has a carbine length gas tube.

    Am I looking in the right areas or could it be something else. Since there are two issues it threw me off a bit.

    Thanks for any advice to save me a bit of time and ammo on testing. Hell, at least the barrel is damn accurate!
    "Education is a weapon whose effects depend on who holds it in his hands and at whom it is aimed." - Joseph Stalin

  2. #2
    Patrolman old11bravo's Avatar
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    Re: AR15 build problems

    Sounds like it may be short stroking to cause the second issue. Lighter buffer than what you currently have will typically remedy this and would be my first try at the fix.

  3. #3
    Sniper MorrisWR's Avatar
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    Re: AR15 build problems

    Would testing the Colts shorter spring help if that is the problem or just going lighter on the buffer? I can pick up a few other buffers though. Ejected round are right around 4 o'clock.
    "Education is a weapon whose effects depend on who holds it in his hands and at whom it is aimed." - Joseph Stalin

  4. #4
    Expert Marksman
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    Re: AR15 build problems

    Try manually cycling it with the different springs. Does the bolt travel further behind the bolt catch with the 10.5" spring? A full inch difference in spring length just seems wrong.

    Sent from my SM-N950U using Tapatalk

  5. #5
    Sniper MorrisWR's Avatar
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    Re: AR15 build problems

    I thought that spring length was excessive also and wondered if they had sold the kit with a rifle length spring. I am going to swap them and try it again next weekend. Manually with either it goes back far enough to have extra space between bolt and catch. Since it already has a light (standard buffer) and that long (and noticeably stronger) spring, I am wondering if it might be moving too fast to always lock back.
    "Education is a weapon whose effects depend on who holds it in his hands and at whom it is aimed." - Joseph Stalin

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