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Thread: 14.5 midlength/failure to lock back

  1. #11
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    I switched to an H Buffer yesterday. Like you... when my 14.5 middy was new it ran everything.... even on an H3 buffer. I ran an H2 for about 1000 rounds.

    But now it's settled into not locking back 100% with .223 ammo.

    The gun still cycles 100%... smooth, and postive ejection.

  2. #12
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    What was the weather temperature when this happened?

  3. #13
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    Quote Originally Posted by markm View Post
    I switched to an H Buffer yesterday. Like you... when my 14.5 middy was new it ran everything.... even on an H3 buffer. I ran an H2 for about 1000 rounds.

    But now it's settled into not locking back 100% with .223 ammo.

    The gun still cycles 100%... smooth, and postive ejection.
    That's a little disappointing. I could feel a difference with the H2 buffer. I was hoping the rifle would loosen up to be able to run a H3 (the H3 had noticeably less recoil when I was testing). My 10.5 started out unable to lock back on a H3 (still cycled reliably) and got to where it could run perfectly with one after about 1000 rounds. Maybe the shorter barrel is more likely to get early gas port erosion?

    Quote Originally Posted by OutlawDon View Post
    What was the weather temperature when this happened?
    Southern Arizona (warm and sunny).
    Last edited by mechelaar; 03-06-11 at 14:21.

  4. #14
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    Okay, here's the update, guys. Just got back from the range.

    I shot XM193 with the H2 buffer and newer 2010 PMags. I did not clean the rifle or add any lube from yesterday. No malfunctions. The bolt locked back 52 out of 52 times. This was following both single shots and strings of fire.

    I am going to chalk this up to some sort of tolerance stacking issue between the older magazine and the LMT Lower. I'll keep my eye on it, to see if it pops back up. For now I'm going to say that the case is closed.

  5. #15
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    Quote Originally Posted by OutlawDon View Post
    What was the weather temperature when this happened?
    That's the only variable I can think of.

    It was hot as hell the first time I started messing with my upper. I'm talking well over 100 degrees when we shot all the video and stuff.

  6. #16
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    Quote Originally Posted by markm View Post
    That's the only variable I can think of.

    It was hot as hell the first time I started messing with my upper. I'm talking well over 100 degrees when we shot all the video and stuff.
    I bought my upper last fall, but didn't get around to putting the gun together until winter. Pretty sure I was wearing a jacket when I tried all the different buffers.

  7. #17
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    I'm glad you seem to have the problem isolated to the Pmags being the possible culprit. I have a similar situation with a different set up but reading this introduces my magazines into the fold as the possible solution.

    Best of luck and keep us posted.
    Tzoid

    Texan raised in " The Peoples Republic of Maryland"

    "RRA- if they came with a blow job I wouldn't take one." - Pat Rogers

  8. #18
    Join Date
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    Things that control bolt lock back when empty:

    Bolt catch...it has to have the full range of travel.
    Bolt catch weight...adding a bolt catch device which adds weight to the bolt catch can make an otherwise good functioning bolt catch stop functioning. Adding weight to it with an aftermarket device slows its upward travel.
    Magazine follower travel and mag spring pressure...... Follower has to rise high enough to lift the bolt catch. Mag spring has to lift the follower enough to catch to bolt catch in the time the BCG is to the rear. Follower might be in 100% condition but if the mag spring can't get it to were it needs to be at the right time it's useless.
    Ammo...if the ammo is so damn weak that it's not making the bolt carrier move ALL the way to the rear where it contacts the very interior end of the receiver extension than the bolt may not lock back nor allow the next round in the magazine to feed into the chamber.
    Chief Armorer for Elite Shooting Sports in Manassas VA
    Chief Armorer for Corp Arms (FFL 07-08/SOT 02)

  9. #19
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    The follower on the older P mags came up higher in the magazine than the newer ones. If the follower is Foliage green you have one of the newer mags and it can be a problem getting the last shot to lock open.
    I'm not sure why Magpul decided to fix something that wasn't broken.

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