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Thread: Failure to Feed..LMT CQB MRP Piston

  1. #21
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    Quote Originally Posted by dcmdon View Post
    That drag is the BC engaging the hammer and cocking it.
    How about after the hammer is cocked (on the first pull) then cycling over and over... the resistance is only for about 3/4 of an inch in the total travel and only after the first in and a half does it start

  2. #22
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    Quote Originally Posted by hoverp View Post
    How about after the hammer is cocked (on the first pull) then cycling over and over... the resistance is only for about 3/4 of an inch in the total travel and only after the first in and a half does it start


    OK I am STUPID... the resistance IS the Bolt carrier riding up over the hammer in the lower I watched the trigger move ever so sligtly to the rear when I cycle the charging handle in the spot. looking at the bottom of th BCG you can see the ramp up to the flat spot that runs forward. It does this even after the hammer is cocked and is laying back in wait. thats what the resistance is.

    BUT I just put in a unmarked carbine buffer that came with my DI 16' LMT barrel that I bought and swapped out the required Piston buffer (H2) for it. big difference in weight....the unmarked is much lighter than the H2
    it still wont lock back on a single round in the mag (new LMT factory or Magpull new)
    and it wont pick up a new round and chamber properly ...shooting new Hornady 75 grain TAP.

    I finally contacted Gene and he wants the upper sent back to him. So I will.

    Thanks guys...
    Last edited by hoverp; 04-10-09 at 11:05.

  3. #23
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    hoverp,

    I'm not sure that Hornady TAP is full power ammo either......That said, have you any or can you get any Prvi 55gr??? That stuff is like butter in my LMT Piston!!!

    Take care and good luck.
    God Bless and good shootin'!!!

  4. #24
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    Sticky, Now Im an AR 15 owner now what info!!!!

    From the Sticky... Many piston ARs suffer from bolt tilt. Bolt tilt is where the carrier bottom side at the rear of it is slammed downward as it cycles, as the carrier tilts downward the first thing the carrier impacts is the bottom of the receiver extension and this causes gouging the receiver extension near the buffer retainer. These gouges can get so bad that the rifle will have some very unusual hard to diagnose stoppages which include short stroking, failures to feed etc. I have a friend who has over 20K rounds through his piston gun and it looked like someone took a rat tail file to his receiver extension. He's also now running an experimental anti-tilt buffer as am I. I'm using this experimental buffer which addresses these tilt problems, and it is working very well at stopping bolt tilt 100% so far. The Primary Weapons conversion does have least amount of tilt for conversion units, mine wasn't bad even before using the anti-tilt buffer but the carrier did remove a little of the finish from the inside of the bottom of the receiver extension. After getting the new anti-tilt buffer I started fresh with a brand new LMT receiver extension to track any changes .

    Standard direct impingement ARs don't have bolt tilt issues because the gas chamber is in the center of the carrier and when the gas is expanded in that chamber this expansion forces the bolt carrier rearward and the bolt forward until the carrier moves far enough rearward that the bolt unlocks and follower the carrier rearward.

    Piston ARs have bolt tilt because they have a solid mass (not gas) impact the top front of the carrier, or they have carrier key which is impacted by the op rod which is mounted high on top the bolt carrier. The natural first movement of the carrier is to cam down slightly before starting rearward. If not addressed this is why there is gouging at the receiver extension near the buffer retainer. Some companies address this with pads at the tail end of the carrier to limit the amount of tilt.



    I think I found part of the problem, please look at the pics, (I hope they come out good) I am getting a serious rub on the buffer tube (just to the left of the retaining pin in the pic)it is really wearing the metal down on the buffer tube lip. also getting bolt carrier strike on the lower part of the buffer tube...se where the gray coating is worn off down to black and even metal inside the tube.
    LMT Piston owners please see if yours look the same !

    Thanks

    Swirl.

    Attachment 2288

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  5. #25
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    Newbi

    LMT has machined a taper into the back bottom of the BCG(see pic above) to address this problem of carrier tilt but, I wonder if all the LMT Pistons internal tubes look like mine? Are they wearing worse or does mine look fairly bad for a few hundred rounds?

  6. #26
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    Dude, that "wear" is nothing to worry about. LMT uses a dry lubricant that eventually goes away with normal use. if it really bugs you, spray some non-fluorinated brake cleaniner down the tube and wash all of the dry lube off, then the RE will be uniform on the inside. I will admit that you have an issue with the rifle, but it is making you waaaaay too paranoid. Get it fixed then shoot the shit out of it.

  7. #27
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    Thats not any wear to speak of.

    Seriously, you're waaaayyy overthinking this. Just box it up and ship it back. Let LMT make it right.
    Its human nature to want to figure things out. I'm the same way. You want to UNDERSTAND the problem. Thats great. But part of what you paid for
    is warranty support. That is unless you enjoy testing and diagnosing the problem. Then have at it.

    Don
    Last edited by dcmdon; 04-12-09 at 21:57.

  8. #28
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    Quote Originally Posted by dcmdon View Post
    Thats not any wear to speak of.

    Seriously, you're waaaayyy overthinking this. Just box it up and ship it back. Let LMT make it right.
    Its human nature to want to figure things out. I'm the same way. You want to UNDERSTAND the problem. Thats great. But part of what you paid for
    is warranty support. That is unless you enjoy testing and diagnosing the problem. Then have at it.

    Don

    Roger that .

    I am new to owning AR's, shot the heck out of M1As and Garands, so I am used to pistons and op rods...just not in the AR config...

    In the pics I want to show you the direct hits the tube is taking at the immediate left of the buffer retaining pin... right at the lip of the 90 degree tube end ...metel on metal ...i wasnt trying to show so much of the inner tube surface.

    but you are right.. I am going to send it back but I also wanted to know from other LMT piston owners if their lower looked the same or worse than mine.

    Thanks .

    Swirl.

  9. #29
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    suggest you bring that point up to LMT also, when you send it back.

    The ARs are a whole different world. I'm just starting to shoot a M1A and an M1Carbine that I've owned for years. I really love the carbine. What a great fun gun.

    I purchased a service grade gun from the CMp. I was underwhelmed when I got it. After speaking with some guys on the internet a couple of months ago I realized the thing looked so bad because it was covered in Cosmoline. After a thorough scrubbing and a few coats of tung oil, the thing is GORGEOUS. Made in 1943. I cant help but wonder what happened to the guy who carried it in WWII.
    Don

  10. #30
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    It appears that LMT doesn't use a RE that is specific to the piston rifle, just an off the shelf LMT extension. Now that the BCG has made its own "chamfer" on the receiver extension, I will put money on that little spot of wear not ever getting worse. I would not worry about it at all and if it ever does become a problem, a new RE is 35 bucks.

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