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Thread: Bolt over base in new LMT MRP

  1. #1
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    Bolt over base in new LMT MRP

    I purchased an LMT MRP complete rifle last week direct from LMT, took it home, cleaned it thoroughly and lubed it up with ALG Go Juice.
    During the first 60 rounds fired, I experienced 3 bolt over base malfunctions (Federal XM193 5.56)
    At approx round 240, I encountered another bolt over base. (Federal American Eagle .223)
    Current round count - 260rnds.

    Magazines were 3 new Lancer 20rounders used randomly. No malfunctions in new Lancer 30rounders.
    Rifle is a stock LMT, with the LMT ebcg and 16" mid-length stainless barrel & car buffer. Stock A2 flash hider.

    I never experienced a bolt over base in any of my BCM or PWS rifles, so I have little idea what I should do. Re-clean it? Run 200 rounds more to break it in?

  2. #2
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    I just went through this with myself.

    I file 13'd my mags and tried again with new Gen M3s. Problem solved.

  3. #3
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    It MUST be the mags.....

  4. #4
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    Why are you running an ebcg? I bought my MRP with an L7D3, never a feeding issue with Okay mags, did break an ejector coil pin though.

    Come to think of it I did have an odd issue with it not locking back, I think the carbine buffer is way light and replaced it with an H2, not a hiccup since. During this early period I remember firing a round, it ejecting, the bolt closing and click, nothing in the chamber. Coupled with the bcg not locking back my thinking was occasionally the bcg was moving too fast to pick up the next round, or lock back after the last round. I went H2.

  5. #5
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    I can't recall if LMT told me to use an H or an H2 buffer, but I believe that they told me not to use a std CAR buffer with a 16" barrel mid-length gas tube/enhanced carrier combo.

    And I only bought the enhanced BCG because it was on sale for less than the std BCG.

  6. #6
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    - Ordered a Geissele Super 42 with an extra tungsten weight.
    - Numbered all mags and will catalog malfunctions (if they appear)
    - Rifle came from LMT with CAR buffer & EBCG - I changed nothing (thus far)


    Thank you guys for the input!

  7. #7
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    Live cartridge or a spent one?
    GET IN YOUR BUBBLE!

  8. #8
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    The extractor of the LMT E-Bolt uses two extractor springs. The two springs are smaller in diameter and longer in length than the standard extractor spring. All too often, the LMT springs are under powered, leading to extraction issues that cause bolt overs. To fix the extraction issues with the LMT E-Bolt I have, I had to make new extractor springs from a take down pin retainer spring. If you do make new springs, don't simply cut them to the same length as the originals. Count the coils and compare the lengths. Add a couple of coils if needed to make the replacement springs just a little bit longer. Not too many extra coils or the springs will bind up.
    The number of folks on my Full Of Shit list grows everyday

    http://i115.photobucket.com/albums/n289/SgtSongDog/AR%20Carbine/DSC_0114.jpg
    I am American

  9. #9
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    mark5pt56 - live rounds

    MistWolf - anyway I can test this? As noted above (I should have made that clear, my mistake) all malfunctions occurred with live rounds. Ejection appears strong, spent brass shows no damage.

    UPDATE - Installed Geissele Super42 in H1 config. I am getting consistent 2'o clock ejection.
    No malfunctions during short range trip (80 rounds) with slow and rapid fire. Will experiment with H2 when I get the time to do a propper evaluation.

  10. #10
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    I think when these are new they are over gassed not because of large port size, more because they are very tight, as in sealed or close tolerance. The carbine buffer amplifies that. With an H2 mine ejects at around 2 o'clock but I really don't place a lot of faith in that, these are geared more for functional reliability vs soft shooting.
    Last edited by LMT/556; 09-25-18 at 16:06.

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