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Thread: Help w/ intermittent FTE/stovepipe issue

  1. #21
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    Quote Originally Posted by steyrman13 View Post
    Is it possible that you lost count and the last 2 rounds of Mk 318 were in fact the PPU as well?
    The PPU is definitely giving you issues on both weapons for sure. The MK318 made it 98 before failure or possibly miss counted 2 rnds and no failures.
    No, I when I went to PMAG #4 there were exactly 7 rounds of Mk 318 left. 6 went on top of 24 rounds of PPU, and the 7th went in a different mag to load the chamber before inserting #4. The first thing I did was remove the mag & all the rounds in it to count & make sure I hadn't somehow stuffed 31 in there. It was 30. Then 25 rounds of PPU went in under 5 rounds of Mk 318, and one 318 in the other mag. Then I repeated the whole unload & count & reload thing again once or twice. Then after taking all the rounds out I switched to PMAG #3 that had worked fine just before I took out #4, only now it did it too. However, when #3 first went south it still had one Mk 318 up the spout and at least one on top in the mag.

  2. #22
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    Quote Originally Posted by steyrman13 View Post
    In the OP the only ammo that caused issues with the LW build was the PPU as well...
    Very true, and it was a big surprise that the 6920 started acting up before I got to the PPU. Nor did it act up the same way, as I never saw any stovepipes on the 6920.

  3. #23
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    OK, based on getting under the hood on the 6920 I'm halfway there on the grease thing.

    I'll preface by stating that Tetra is not like the old school military rifle grease. It's a lot closer to liquid than that. Also, in addition to going over 800 rounds on a single application of it in the 9620, I also once went about 500 in a CZ P-01 on a 3 month old application of it, and over 1600 in a Beretta 92 over the course of a couple months on a single application of it. The directions on the package say to buff it dry, but I've always left a light coat looking wet (as grease would traditionally be used). Until now, this has worked like a champ in all my semi-autos.

    That said, though, the 9620 sat much longer than any of the above. I wiped out the inside of the upper before sending it to ADCO and reapplied Tetra to that after it came back. However, I just took out the BCG before shipping the upper and put it in a plastic bag to wait (it was only 6 days - ADCO was impressively fast). Because it still looked wet, I just dropped the BCG back in and went to the range.

    Cleaning it, I found the BCG unusually "gummy". I've cleaned lots of BCG's that had been lubed with Tetra and then fired, and they usually just clean right up with a few squirts of gunscrubber & maybe a little toothbrush action, then a wipedown with CLP for rust prevention. This took a lot more solvent & elbow grease. So, I think what happened is the Tetra set up over time and the 6920 was acting more or less like it was dry, despite the Tetra looking wet.

    Hopefully Thursday I'll get the following done...

    Test the two new ammos (Mk 318 & PRVI M855) in the bone-stock 6520, starting with the mag lockback test (and the carbine freshly cleaned & lubed to eliminate that variable).

    Test the 6920 (freshly cleaned & lubed) with known good ammo, again starting with the mag lockback test. I'll fire XM193 & Q3131a until I've gone 200 or run out or hit big trouble again, then if it looks good try the new ammos again.

    While I have both BF CLP and Slip 2000 (which I've never used yet) on hand, to not introduce any new variable I'm going to stick with the Tetra for these tests (just freshly applied after thorough cleaning). I'm thinking that once I get through this, I'll try the SLIP 2000 in the 6920.

    If this works out, then I can get back to figuring out why the new LW build is stovepiping.
    Last edited by Barnacle Bill; 08-20-13 at 09:22.

  4. #24
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    Get some non-chlorinated brake cleaner and clean the tetra out of the entire upper and BCG. Then lube with the slip 2000 test. It is a known performer and by re using tetra you will be wasting ammo and time again.

  5. #25
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    It sounds like you are on the right track. I agree with using non-chlorinated brake cleaner and thoroughly cleaning the upper.

    I would use some kind of oil, Break Free CLP, Mobil 1 motor oil, etc., to test the carbine after cleaning. If the issue is resolved, you can always test the more modern lubricants later.

  6. #26
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    The new synthetic-safe Gunscrubber is functionally equivalent to non-chlorinated brake cleaner, but several cans of it currently reside in my basement.

    I guess I can try the Slip 2000 for the tests, although that becomes a new variable. It may be a known performers generically, but I never used any before myself (bought it back in the winter after seeing on a video how well it does in sub-zero temperatures, but never got around to trying it before the weather warmed up).

  7. #27
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    OK next installment...

    The 6520 (with the grease cleaned out & relubed with Slip 2000 EWL) digested 100 each of the Mk 318 & the PPU M855, without any trouble at all. Part of that was doing the lock back test with a mag with only one round in it, 10 times with each load using 5 different mags.

    The 6920 (with the grease cleaned out & relubed with Slip 2000 EWL) digested 100 each of first Win Q3131A & then the Mk 318, without any trouble at all. Part of that was doing the lock back test with a mag with only one round in it, 10 times with each load using 5 different mags.

    Then I did the lock back test 10 times on the PPU, no problems.

    Then I shot off a 30 round mag of the PPU, again no problems.

    Then I put in a second 30 round mag of the PPU. Bang-click... short-stroked. Cycle the action to chamber a round manually...bang-click...short-stroked. Repeat one or two more times, same result.

    To avoid breaking open another sealed 200 round pack of the PPU, I then took rounds out of the mag to put one each in the other mags I had with me to run the single shot lock back test. 2 or three times in a row it failed to lock back. Then two or three times in a row it locked back. Then I reinserted the mag I had in when this started, which at that point had 20ish rounds still in it. It functioned properly, down to lock back on empty.

    At that point, with about 500 rounds fired through the two carbines in about 3 hours, I called it a day.

    So, what happened with that run of the PPU not working right, and can I assume it's just the ammo and I can rely on the carbine if I load it with Mk 318?

  8. #28
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    Sounds like the ammo is the problem. I've never had issues with PPU ammo. I'd shoot the rest in another carbine or just sell it and buy Federal instead.
    Not sure about you guys, but I'm only here for the free food and open bar.

    Certified Smith & Wesson M&P Armorer
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  9. #29
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    Quote Originally Posted by bluejackets92fs View Post
    Sounds like the ammo is the problem. I've never had issues with PPU ammo. I'd shoot the rest in another carbine or just sell it and buy Federal instead.
    I haven't had much trouble before this. I had a CMMG that didn't like PPU 75gr OTM, although it ran fine in other AR's. All this shooting of it has put a pretty big dent in my PPU M855 stash, with only one or two 200-rnd packs left now. I think I'll replace it with Federal as you suggest, since that is starting to show up online at reasonable bulk prices. I have a whole bunch of PPU M193, but I haven't seen any issue with that (in all honesty I haven't shot a lot of it yet, though). If I was going to use it for anything besides practice, I wouldn't want M855 but my understanding is that Mk 318 is more or less the same trajectory and the 9620 now has an ACOG on it with an M855 ballistic reticle.

    So, next back to the original issue in this thread, the LW carbine build and its stovepipes. I have a BCM bolt rebuild kit on hand I can install, but since it worked fine with the Mk 318 and only started acting up when I switched to the PPU M855, maybe the thing to do is just shoot a bunch of other ammo and see what happens. Interestingly, the 6520 had been zeroed at 50Y with HSM's 75gr TAP-clone load, and the irins only need one click to the right from that zero to be on with the Mk 318. I have a lot of that stuff, so maybe I'll see how it does in the LW. Or, I can drop the bolt from the 6520 into the LW and see if that fixes the stovepipes (the 6520 didn't have any problems through 100 rounds of the PPU M855).

  10. #30
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    Just for shits and giggles. Check your rings on your BCG and make sure the slots haven't lined up.
    Not sure about you guys, but I'm only here for the free food and open bar.

    Certified Smith & Wesson M&P Armorer
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