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Thread: A bit of help with this malfunction.

  1. #41
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    First day of class today and I had problems pretty much from the get go. Thankfully LAV was in good spirits so I didn't get picked on too much.

    The main problem is that the buffer spring is far to weak. My assumption is that the spring has been wearing out over time. This lower has only seen about 5K rounds over the past year so I don't think it should already be worn. However case remains that there were times when rounds would barely even seat because the spring didn't have enough force to ram them forward. I pulled the spring out of my other gun and the 10.5 ran like a champ for the rest of the day. It is still running a bit to fast according to Larry but that is something I can tweak later with a heavier buffer.

    Thanks for all the help guys.

  2. #42
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    Glad you got it to run.

    How long (in inches) is the weak buffer spring?

    IIRC, 5k is about all you should expect out of it.


    https://www.m4carbine.net/showthread.php?t=91043
    Last edited by Clint; 12-20-11 at 01:17.
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  3. #43
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    springs are one of the little things that many people undervalue and skimp on. It's one of the few parts I make sure are Colt OEM.

    Glad to hear you were able to get it running along.

  4. #44
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    Quote Originally Posted by kwelz View Post
    First day of class today and I had problems pretty much from the get go. Thankfully LAV was in good spirits so I didn't get picked on too much.

    The main problem is that the buffer spring is far to weak. My assumption is that the spring has been wearing out over time. This lower has only seen about 5K rounds over the past year so I don't think it should already be worn. However case remains that there were times when rounds would barely even seat because the spring didn't have enough force to ram them forward. I pulled the spring out of my other gun and the 10.5 ran like a champ for the rest of the day. It is still running a bit to fast according to Larry but that is something I can tweak later with a heavier buffer.

    Thanks for all the help guys.
    Glad to hear you have your gun working. RE action springs, if you have a work bench, find out what the recommended minimum free length is and mark it on a table. This makes it easy to check whenever you disassemble your weapon.

  5. #45
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    Ran the search and and came up on this thread. I had this exact issue happen today twice while checking zero on two different uppers (but the same lower).

    Both times were with PMC Bronze 55gr and the same magazine (PMAG). Upper #1 is a brand new (first time firing) BCM 16" LW, upper #2 is my assembled Centurion CHF LW 16." Malfunction #1 happened on the second to last round, malfunction #2 happened on the last round of the magazine.

    Both times they happened, it appeared that the cartridge was partially up the feed ramp, with the bullet half way into the chamber, but the bolt had squashed it into the feed ramp. Upon clearing, both casings had large dents where the bolt hammered them.

    The lower has been fired/cycled a few thousand times. This very malfunction happened twice with Hornady 55gr training ammo way back when the lower was brand new (and I'm thinking those malfunctions happened with the same magazine....but I wasn't smart enough to track it), but has worked fine ever since with PMC Bronze and just about anything else I've fed it.

    I'll have to check the action spring length. I'm in the market for swapping to an A5, so this might just be the opportune time.
    "Man is still the first weapon of war" - Field Marshal Montgomery

    The Everyday Marksman

  6. #46
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    I never did get back to this thread but while the spring made it better it didn't completely fix the issue. I had more issues on day 2 of the class and ended up breaking out my Novekse 14.5 to finish up the weekend.

    After the class we pulled the spring and it is a good 3/4 of an inch shorter than the ay other spring we looked at. I have replaced it with a high power spring but haven't had time to do any testing yet due to the holidays. If all else fails we will do a complete tear down and rebuild of the weapon.

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