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Thread: 7.62 AR-10 mild Kaboom

  1. #11
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    Quote Originally Posted by markm View Post
    BRT reduced gas port gas tube installed.

    powder is Varget.
    Hmmm. 50/50 mixed suppressed port, or low back-pressure 7.62 suppressed port? What suppressor?

    The original DPMS AP-4 with a 7-inch carbine gas tube put some un-godly stress on brass and the bolt carrier group. I'm not sure if anyone tried suppressing those.

    LMT's mid-length gas tube allows the gas block to be protected under the rail. The British (with their L129A1) shoot issue 147-150 grain 7.62 NATO and 155-grain Green Spot Match -- they're not going to show undue extreme pressure signs. The British use a Surefire SOCOM RC suppressor, which I believe is a reflex. Are you shooting something long and efficient with higher back-pressure (like a Silencerco Harvester)?

    My guess is the British aren't going to see or report pressure signs and case failures because they don't own guns, nor hand-load like Americans. We're going to shoot 168s (for precision) and 175s and 185s for precision past 600 yards. Load long-heavy bullets with a longer bearing surface (like a 208) and you're going to add even more pressure.

    It didn't matter that it was a MEN case -- it probably could-would have happened with thick-walled Lake City as well.

    Even if LMT sends you a completely new upper, I'd only fire the mid un-suppressed (or limit to Ball and 155s) and cut down or build a rifle-gas 18- or 20-inch barrel.

  2. #12
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    Stupid question… Do ya think this separation would have happened in another firearm, say a bolt gun?
    Believe it’s particular to conditions exclusive to a gas gun?

  3. #13
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    Particular to gas- or piston-operated systems with efficient suppressors and short gas tubes, or a roller-delayed blowback, suppressed short barrel 7.62 HK.

  4. #14
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    Quote Originally Posted by sinister View Post
    What suppressor?
    Sig Sauer 7.62 suppressor with a mount attachment. Fairly good number of baffles in sig's cans.

    Quote Originally Posted by SFree View Post
    Stupid question… Do ya think this separation would have happened in another firearm, say a bolt gun?
    Believe it’s particular to conditions exclusive to a gas gun?
    Hard to say. I mean... these 7.62 gas guns are pretty harsh on the ammo/brass. Maybe it was a bad piece of brass combined with all the other unfavorable ingredients in the recipe.
    "What would a $2,000 Geissele Super Duty do that a $500 PSA door buster on Black Friday couldn't do?" - Stopsign32v

  5. #15
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    Oh, yeah -- SIG suppressors are REALLY good.



    The good news is Pappabear went first-class with both the rifle and suppressor.

    The "Iffy": the mid-length gas system didn't do you guys any favors.

    For those interested, 16" Mid:



    18" Rifle:


  6. #16
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    I think He has a rifle barrel too. May have to do some re-configuring... I know he doesn't like shooting unsuppressed guns.
    "What would a $2,000 Geissele Super Duty do that a $500 PSA door buster on Black Friday couldn't do?" - Stopsign32v

  7. #17
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    Looks like a place for a custom bbl. Could you have a 16” with rifle length gas tube? D. Wilson… calling D.Wilson…
    Last edited by SFree; 09-07-21 at 22:34.

  8. #18
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    LMT's rifle barrels have the potential to be really precise with the long MWS clamping surface. The problem they have is that big surface makes for a heavier upper (and rifle, overall).

    The 20-incher can be shortened and threaded.

    I don't know if LMT sells their barrel extension / gas tube holder (cassette?) to make custom barrels from blanks (a good machinist-gunsmith can then use a standard AR/ big AR gas block and gas tube).

    Standard:




    This fella turned a custom stainless sleeve to use an 18-inch Fulton Armory 1-10 Criterion barrel in his MWS:





    He says, "The extra length on the gas system was very beneficial. The brass no longer looks like the extractor is trying to tear the rim off."

    It makes 10-shot groups like this:



    Another:



    It looks like Marvin Pitts at Nefarious Arms has done them before:


  9. #19
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    Cutting down a rifle barrel to get a longer gas system strikes me as ideal. I'm curious how "they" got the gas block off of the barrel in that last pic. I heard LMT has a special tool for installing them.
    "What would a $2,000 Geissele Super Duty do that a $500 PSA door buster on Black Friday couldn't do?" - Stopsign32v

  10. #20
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    It looks like the two tools Marvin has above the barrel aligns the gas block with the port and upper receiver hole (left tool) while the second is a castle nut tool (to tighten the gas block against that shoulder butt).

    The interesting thing about LMT's gas port is it's machined on a back-sloping angle (vice 90 degrees to the bore).

    D(ave) Wilson does the LMT 5.56 MRP barrel conversion, so the 7.62 MWSs should be possible.

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