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Thread: Trouble Shooting an AR-15

  1. #1
    Tool & Die Maker
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    Default Trouble Shooting an AR-15

    Met an old timer months ago with a new AR-15 Blackout at the shooting range. He was constantly struggling with misfires and bolt jambs. He is the guy that introduce me to these bolt free tools.

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    Bumped into the guy several times. I told him it appears something is wrong with the firing chamber. The bolt would fail to close by at least 1/8". He finally returned the upper receiver to the manufacturer and they replaced the barrel. Met the guy today and he is struggling with his stuck bolt again. He said the new barrel didn't change anything. We tried one of my plastic magazines in this gun and no change. I got to thinking I had my AR 223 with me so we installed my lower receiver under his 300 aac upper and his bolt. Significant improvement, I thought we had it then after 6-8 rounds it jammed again. Next we tried my bolt and my receiver under his upper, no change. We did determine the bullet does properly seat in the firing chamber. The bolt itself is sticking. Actually the bolt fails to close. I tinkered with the charge handle, opening and closing the bolt, eventually the bolt will go closed and fire properly but chances are it will fail to cycle.

    My theory is the upper receiver has issues. Is there any chance the bolt is not concentric with the barrel or is it something else? The bolt has those gear teeth that mesh with gear teeth in the barrel. I think the problem is right there. I recall the barrel had an indexing pin that engaged with a slot in the receiver,
    wonder if the slot is not properly indexed, or the slot that indexes the bolt.

    opinions and theories welcome
    Last edited by jim Glass; 11-06-2018 at 02:09 PM.


  2. #2
    Senior Member kyratshooter's Avatar
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    Default

    My first thought is a light buffer spring and not enough lube.

    Take the upper off the lower and run the bolt in and out of engagement and see if it cycles freely.

    If the bolt and carrier cycle freely, and the cartridge is spec to the chamber there are other issues.

    Does it jam when the first round is cycled by hand or only when being fired?

    Have you hand cycled a full magazine of rounds through the rifle?

    Here's a thought, how is it shooting when it does fire? What is the accuracy?
    If you didn't bring jerky what did I just eat?

  3. #3
    Tool & Die Maker
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    Default

    Was looking at my 223 after I got home. Had the upper receiver removed to I could bore sight my homemade gun sights. Studied carefully how the bolt actually works (how it turns and locks and unlocks). I would like to look at the problem AR the same way but I don't have access to it. I think the problem is in those locking gear teeth, a timing issue or something.

    We hand loaded bullets into the firing chamber and the bolt would not close. We thought it was the firing chamber, the bullets were not fully seated. Today we determined the bullets were fully seated and the bolt still may or may not close. We had to use that tool 5-6 times to free the bolt. By the way, I sold 3 of those tools today and have orders for more of them.

    Was sure swapping parts of my AR with his would have isolated the problem but it did not. Although my parts worked better than his.

    Take the upper off the lower and run the bolt in and out of engagement and see if it cycles freely.
    We need to do that.

    If the bolt and carrier cycle freely, and the cartridge is spec to the chamber there are other issues.
    Cartridge is to spec.

    Does it jam when the first round is cycled by hand or only when being fired?
    All times

    Have you hand cycled a full magazine of rounds through the rifle?
    It usually won't hand cycle although there was improvement using my receiver.

    Here's a thought, how is it shooting when it does fire? What is the accuracy?
    The owner of the AR is nearly blind, can't go my accuracy.
    Last edited by jim Glass; 11-06-2018 at 10:05 PM.

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