Requesting input on a AR15 malfunction.

Requesting input on a AR15 malfunction.

This is a discussion on Requesting input on a AR15 malfunction. within the Defensive Rifles & Shotgun Discussion forums, part of the Related Topics category; I need help diagnosing a malfunction with an AR15. First, what I'm working with. -18" Ballistic Advantage barrel, with rifle length gas system -LaRue Tactical ...

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Thread: Requesting input on a AR15 malfunction.

  1. #1
    Member Array HazeGray's Avatar
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    Requesting input on a AR15 malfunction.

    I need help diagnosing a malfunction with an AR15.

    First, what I'm working with.

    -18" Ballistic Advantage barrel, with rifle length gas system
    -LaRue Tactical MBT-2S trigger, with the heavier trigger spring installed
    -Spike's Tactical rifle length gas tube
    -BCM bolt carrier group
    -Mil-spec 6-pos receiver extension
    -Yankee Hill Machine gas block (YHM 9384)
    -Tubb Precision AR-15 Stainless Steel Buffer Spring (model: ARBUF)
    -Ammunition: Reaper Outdoors Controlled Chaos 223 Remington 55 gr, Wolf steel cased 55gr, GA Arms 55gr as well as a variety of my hand loaded 55 and 62gr FMJ.


    This is what is happening, approximately after every third or fourth round.
    Requesting input on a AR15 malfunction.-img_2430.jpg

    These are the factors that I believe I can eliminate:

    Although my gas block is a clamp on type, I do not think it or my gas tube is causing my rifle to short stroke (i.e. insufficient gas); and this is why. Five out of five consecutive times, I loaded one round into a magazine and the bolt locked to the rear.
    The gas key on my bolt carrier group is properly staked and I do not see any carbon build up along the bottom of it that would indicate it is leaking.

    I also don't think that the culprit is magazine related, as this malfunction repeated with three different Magpul P-mags and an aluminum USGI Brownells mag.

    Lastly, I have increased the weight the buffer from the standard 2.8 oz up to 4.6 oz by swapping out two steel weights for two tungsten weights with one steel remaining.

    I built this AR15 over the course of the past two years, and thus far I have only made it to the range 3 to 4 times. It is my fifth build and the one only with problem of this sort.

    Thank you in advance.

  2. #2
    VIP Member Array Chuck R.'s Avatar
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    Ammo?

    The picture shows what appears to be 2, possibly 3 different manufacturers. Anything systemic by manufacturer?
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  3. #3
    Member Array HazeGray's Avatar
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    Primers are fine, with both factory ammo and my hand loads.

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    Member Array HazeGray's Avatar
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    Quote Originally Posted by Chuck R. View Post
    Ammo?

    The picture shows what appears to be 2, possibly 3 different manufacturers. Anything systemic by manufacturer?
    Yes, I wanted to see that the malfunction happens with a variety of ammo. That pic represents the worst looking rounds.

    Also, the barrel is crazy accurate.

  6. #5
    VIP Member Array Bad Bob's Avatar
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    What is the exact failure? Load, fire, extract eject?
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    Member Array HazeGray's Avatar
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    Quote Originally Posted by Bad Bob View Post
    What is the exact failure? Load, fire, extract eject?
    I meant to put that in my original post. I had failures to extract and other jams where the round did not feed into the chamber properly.

  8. #7
    VIP Member Array Bad Bob's Avatar
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    Quote Originally Posted by HazeGray View Post
    I meant to put that in my original post. I had failures to extract and other jams where the round did not feed into the chamber properly.
    Failure to extract- look at the extractor, ensure you have the upgraded extractor spring. Check the chamber for dirt, burr's etc. Check your gas block for proper alignment,( seems you ruled that out already). The gas generally just unlocks the bolt. It could be the ammo. I would try some factory new ammo, ensure that you are using small base dies for your loads.

    What chamber does your barrel have? 223, 223 Wylde, 5.56?

    Failure to feed is almost always the magazine.
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    VIP Member Array Chuck R.'s Avatar
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    How much did you shoot it with the standard weight buffer??

    The rifle gas length should work well with the standard buffer. When diagnosing stuff I like to go back to as close to the "standard" as I can. So I would try it with the standard buffer with a standard carbine spring. Then try variables one at a time.
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  10. #9
    Member Array HazeGray's Avatar
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    Quote Originally Posted by Bad Bob View Post
    Failure to extract- look at the extractor, ensure you have the upgraded extractor spring. Check the chamber for dirt, burr's etc. Check your gas block for proper alignment,( seems you ruled that out already). The gas generally just unlocks the bolt. It could be the ammo. I would try some factory new ammo, ensure that you are using small base dies for your loads.

    What chamber does your barrel have? 223, 223 Wylde, 5.56?

    Failure to feed is almost always the magazine.
    It is chambered in 5.56 with 1:7 twist.

    I've had this problem occur with a variety of magazines, P-mags and USGI.

    Since I've posted this, I put on new gas rings.

    I'm going to order the BCM extractor upgrade kit as well.

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    Member Array HazeGray's Avatar
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    Quote Originally Posted by Chuck R. View Post
    How much did you shoot it with the standard weight buffer??

    The rifle gas length should work well with the standard buffer. When diagnosing stuff I like to go back to as close to the "standard" as I can. So I would try it with the standard buffer with a standard carbine spring. Then try variables one at a time.
    Adding the tungsten weights didn't do very much. Once I replaced one steel weight for a tungsten, it smoothed the recoil a tiny bit. I still had the problems and swapped out he 2nd steel weight. It is now almost as smooth as my A4 clone in terms of recoil.

  12. #11
    VIP Member Array Bad Bob's Avatar
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    Quote Originally Posted by HazeGray View Post
    It is chambered in 5.56 with 1:7 twist.

    I've had this problem occur with a variety of magazines, P-mags and USGI.

    Since I've posted this, I put on new gas rings.

    I'm going to order the BCM extractor upgrade kit as well.
    Gas rings are not the problem. I may even run without them.
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  13. #12
    Member Array kenboyles72's Avatar
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    Could be a feed ramp issue. Look in the chamber and check to see if the notches are lined up correctly.

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    VIP Member Array OldVet's Avatar
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    I did not see where you mentioned what upper or lower receiver you used.

    I recently built an AR in 6mm mongoose caliber and had much the same problems as you, althought I had more fail to eject than fail to extract. Same feeding problems with the same dented cases. Long story short, I used an Aero Precision upper receiver on an Armalite lower and there is some tolerance rejection that made them incompatible. I built a lower with an Aero Precision lower receiver and everything functioned fine. The Armalite lower works 100% with its Armalite upper also. But it and the aero precision upper just do not play well. Magazine brand or capacity had no positive affect. Ammo (all reloads) had no positive affect. I finally used one of my son's lowers and the upper ran fine. I'd recommend slapping on a different lower and see if results are better.

    I also removed the o-ring from the extractor spring and all the little bits of brass on the bolt face went away. Now as long as I keep the empty case catcher aligned right, the gun runs like a Swiss clock.
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    VIP Member Array OldChap's Avatar
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    Just my tired old eyes. but the two cases on the right do not look like 5.56 cases. Maybe an optical illusion. Have you measured them with calipers?

    Just a few places to look:

    Stacking tolerances between upper and lower (as @OldVet mentioned) although these are really beyond the ability of us to measure,

    Feed ramps for correct configuration and mating, (as the illustration above)

    Magazines (including followers), this and poorly toleranced reloaded ammo is most likely the culprit.

    Go back to a stock M4 spring and buffer.

    This doesn't appear to be an extractor issue. The cases you show that are the most badly dented did not fire. The extractor wouldn't cause that unless they're hitting the receiver outside the chamber.

    And for continuity, buy some quality factory loaded ammunition - no "factory" reloads. Even personally reloaded ammo is not ideal when you're troubleshooting.
    "The difference between genius and stupidity is that genius has limits."

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    VIP Member Array OldVet's Avatar
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    By failed to extract, you're saying the extractor slipped off the rim and left the case in the chamber? Was the rim chewed up where the extractor held it?

    Or was it a fail to eject the empy case and the next round jammed into the empty?

    My mongoose did practically everything wrong, from fail to lock back to fail to eject to fail to feed. Improper case head spacing was part of the problem. Slight under gasing was part. But the main culprit was the incapatibility of the Armalite lower with the Aero Precision upper.

    Which direction do your cases eject in relation to your ejection port? 3-4 o'clock is ideal. More aft is leaning toward under gased, more toward 1-2 o'clock is over gased.
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