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Thread: rifle length gas, 16" barrel

  1. #21
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    That doesn't exactly count...

    I'm sure you were just teasing, but for clarity:

    Each cartridge has a different pressure vs time curve.

    For rifle cartridges, the peak pressure is similar, but the duration or length is the primary difference.

    This curve directly affects the operation of the gas system and drives the optimal range of gas system lengths.

    An easy example is the 300 BLK, which has one of the fastest/shortest curves of any cartridge we're interested in.

    Useable configurations are pistol or carbine length gas system, even up to 16" barrel length.


    Quote Originally Posted by lifebreath View Post
    Well, it's 16" and rifle length gas .... but it's 308.

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  2. #22
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    The standard port for a 20" barrel is .093".

    I think about the shortest I'd go again is 18". I have experience with 17 and 18" barrels and rifle length gas systems.

  3. #23
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    There's also the intermediate gas system available

    Sent from my SGH-T999 using Xparent BlueTapatalk 2

  4. #24
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    Yes... we did an Intermediate gas system at Vltor, as I recall John offered it for a while - it was a very nice shooting 18" barrel really.
    Please let me know if I have offended you...
    I would like to move on to my next task.


    I provide legal consultation and training - specializing in the Law of Gravity.

  5. #25
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    Kino, I wonder what PSI we're looking at inside the BCG? If port pressure is well over 20KPSI, how much of that actually makes it into the carrier? By the time it gets there, after having expanded into the volume of the gas tube and carrier expansion chamber, plus, by that time-- I presume-- the bullet has departed the barrel and barrel pressure is dropping......

    I tell guys, just don't hold your fingertip over those carrier exhaust holes while firing.....

    BUT..... I have held carboard right on top of them while firing to get a feel for how much hell is coming out of them-- all I got was some dark smudges, no holes blown through or anything like that. My guess would be that it is hundreds, not thousands of PSI in there-- at least it is greatly reduced from whatever port pressure is in a given setup.

  6. #26
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    The Army M16 test documents show pressure inside the BGC is a curve that peaks around 2500 psi.

    The general shape of the curve is quite similar to the chamber pressure in the barrel.

    Quote Originally Posted by Ned Christiansen View Post
    Kino, I wonder what PSI we're looking at inside the BCG? If port pressure is well over 20KPSI, how much of that actually makes it into the carrier? By the time it gets there, after having expanded into the volume of the gas tube and carrier expansion chamber, plus, by that time-- I presume-- the bullet has departed the barrel and barrel pressure is dropping......

    I tell guys, just don't hold your fingertip over those carrier exhaust holes while firing.....

    BUT..... I have held carboard right on top of them while firing to get a feel for how much hell is coming out of them-- all I got was some dark smudges, no holes blown through or anything like that. My guess would be that it is hundreds, not thousands of PSI in there-- at least it is greatly reduced from whatever port pressure is in a given setup.
    Black River Tactical
    BRT OPTIMUM HFCL Barrels - Hammer Forged Chrome Lined 11.5", 12.5", 14.5"
    BRT OPTIMUM Barrels - 16" MPR, 14.5" MPC, 12.5" MRC, 11.5" CQB, 9" PDW
    BRT EZTUNE Preset Gas Tubes - CAR and MID
    BRT Covert Comps 7.62, 5.56, 6X, 9mm
    BRT MarkBlue Gas Tubes - BRT EXT, EXC and PDW Lengths
    BRT MicroPin Gas Blocks - .750" & .625"
    BRT MicroTUNE Adjustable Gas Blocks
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  7. #27
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    Would not have guessed that much but..... I could only guess. Doesn't sound unreasonable.

  8. #28
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    Quote Originally Posted by ChicagoTex View Post
    From what I've heard/read that's the issue. The dwell-time for a rifle length gas tube and 16" barrel is too short, so you have to seriously open the gas port to compensate in order to get proper reliability. Unfortunately, doing so pretty much negates the benefit of using a rifle length gas system IMO.

    Mid-length is the way to go on 16"ers.
    This, right here.
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  9. #29
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    I have cut a good many department A-1's to 16" and got away with it..... I thought. In test firing they were 100%. But test firing is not the same as a 1000 round class and does not take into account the condition of the rifle and all its component parts a year or five down the road.

    It works as long as the rest of the gun / ammo symbiance (I think I just made up that word) is optimal. Sprinkle in some weaker ammo and/or worn gas rings that otherwise would have gone unnoticed, and they will be.... noticed, in the form of malfunctions.

    So, I don't do that no more.

  10. #30
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    Ned,

    what size gas ports did you use on those 16" rifles?
    Last edited by Clint; 09-18-13 at 20:27.
    Black River Tactical
    BRT OPTIMUM HFCL Barrels - Hammer Forged Chrome Lined 11.5", 12.5", 14.5"
    BRT OPTIMUM Barrels - 16" MPR, 14.5" MPC, 12.5" MRC, 11.5" CQB, 9" PDW
    BRT EZTUNE Preset Gas Tubes - CAR and MID
    BRT Covert Comps 7.62, 5.56, 6X, 9mm
    BRT MarkBlue Gas Tubes - BRT EXT, EXC and PDW Lengths
    BRT MicroPin Gas Blocks - .750" & .625"
    BRT MicroTUNE Adjustable Gas Blocks
    BRT CustomTUNE Gas Ports

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