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Thread: 11.5” Mid Length Barrel Discussion

  1. #11
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    I'm really curious as to what these things offer over a properly built and ported carbine gas system.



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  2. #12
    FaxonNathan Guest
    Quote Originally Posted by Clint View Post
    Ray,

    Your analysis looks good so far. (You may want to double check your estimates for the 12.5" length. I have that at .150ms. )

    There is far more involved than just dwell time.

    There is also the blowdown time and pressures at the gas port and muzzle.

    Together these form the overall pressure curve.

    The total area under the curve ( pressure x time ) sets the available gas drive to cycle the weapon.

    The gas port size regulates the flow and effectively scales down the total gas drive.

    The gas tube length adds delay to the start of the cycle.

    The total cycling mass ( buffer + BCG + 1/2 spring ) affects the acceleration of the carrier and affects the start of extraction.

    The start of extraction relative to when the bullet exits the muzzle and pressure drops rapidly is also an important factor.
    A solid analysis.

    Fortunately, the pressure of 5.56 (and even .223) is capable of driving a standard AR-15 without issue using mid and 11.5" gas ports.

  3. #13
    FaxonNathan Guest
    Quote Originally Posted by Iraqgunz View Post
    I'm really curious as to what these things offer over a properly built and ported carbine gas system.
    Primarily, a longer cycle time and reduced perceived recoil (when used with an adjustable block, which could also be said of any gas system).

  4. #14
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    From what I've seen, I would be hesitant about a conventional mid length gas barrel in a 11.5" 5.56 suppressed only gun for generic purposes. There are too many variables, the stretch is too far in gas system length. Slightly shortening this to something similar to a 1" extended system does offer some gain. Oversizing the port with an adjustable gas block may produce acceptable results for some, but others may really want a dedicated port without user adjustments for them. If one used a non adjustable block, could their span of function be reduced? Some, with a limit of choices of ammunition and sound suppressor for use be a possible reduction or gain in span of operation?

  5. #15
    FaxonNathan Guest
    Quote Originally Posted by tom12.7 View Post
    From what I've seen, I would be hesitant about a conventional mid length gas barrel in a 11.5" 5.56 suppressed only gun for generic purposes. There are too many variables, the stretch is too far in gas system length. Slightly shortening this to something similar to a 1" extended system does offer some gain. Oversizing the port with an adjustable gas block may produce acceptable results for some, but others may really want a dedicated port without user adjustments for them. If one used a non adjustable block, could their span of function be reduced? Some, with a limit of choices of ammunition and sound suppressor for use be a possible reduction or gain in span of operation?
    If one does not use an adjustable gas block, their span will be the same. Recoil will increase over time (like all barrels as gas ports wear).

    We're not claiming (or marketing) this barrel to be for everyone. This is very much for advanced users who understand the AR in-depth and the benefits and trade-offs that come with this configuration.

  6. #16
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    Quote Originally Posted by FaxonNathan View Post
    We're not claiming (or marketing) this barrel to be for everyone. This is very much for advanced users who understand the AR in-depth and the benefits and trade-offs that come with this configuration.
    Rut Row. Not an advanced user here, but I understand this is an experiment so to speak.

    It is known that the shorter dwell time means less flexible with respect to ammo choices. To that end, if you wear belts and suspenders the 20R should be your SHTF weapon.

    Technically anything else accepts more risk of not working with pickup ammo should that become a need. For me and reasonable scenarios, a 12.5C is my go to.

    For this project, I have not decided what ammo to tune it for. My cheapest is Wolf Gold 55gr (Taiwanese brass cased).

    The other wild card here is also the fact that heavier and slower ammo means more Dwell Time! If I cannot get the 11.5M reliable with 55gr ammo then I will try the 77gr Mk262 clone ammo.

    My FIL has a plain vanilla 11.5C BCM with an FSP. I will function test the Faxon barrel unsuppressed and will try to shoot these uppers together.

  7. #17
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    In a compare and contrast scheme of looking at things like a suppressed only 11.5" 5.56 AR some things can become clear, or clearer. A carbine length gas system and with a conventional carbine H2 action work within a span of reliable function is able to run well with a dedicated can and ammunition, with a properly dedicated port. Some cans and ammunition may need some tweaks in porting to compensate for their issues, normally not by much.
    There are some timing issues that are an caused from the base system that unfortunately are not avoidable, but workable solutions.
    If one looks at the first example as a baseline, it is just that, a reference, a way to make an appropriate relevance to in a comparison.
    Due to the issues of insufficient timing for some events, a slight, but preferable delay may be added to the system by lengthening the distance to the gas port from what it is in the carbine gas conventional system to help compensate a portion of the timing issue. The question is then, how long to extend the gas system. As a reference, a baseline of the first example carbine gas and H2 carbine was used.
    Adding a half inch in gas system length resulted in almost no change in the difference in action velocity comparing multiple examples.
    Adding one inch resulted in almost no change, except for a select few extremes.
    Adding 1.5" makes a larger difference in possible carrier speeds, by a fair margin.
    Given the possible span of proper operation, with all of varieties of the ammo, selected can, etc. I would be hard pressed to recommend the mid gas 11.5" suppressed only setup over the conventional carbine, or carbine +1" gas system.
    There are other beneficial ways to improve the timing somewhat. A rifle like action buffer and rifle spring actually broaden the range of operation more than the baseline. The results of the rifle like action system with a carbine gas or carbine +1" could be noteworthy.

  8. #18
    FaxonNathan Guest
    Quote Originally Posted by Rayrevolver View Post
    Rut Row. Not an advanced user here, but I understand this is an experiment so to speak.

    It is known that the shorter dwell time means less flexible with respect to ammo choices. To that end, if you wear belts and suspenders the 20R should be your SHTF weapon.

    Technically anything else accepts more risk of not working with pickup ammo should that become a need. For me and reasonable scenarios, a 12.5C is my go to.

    For this project, I have not decided what ammo to tune it for. My cheapest is Wolf Gold 55gr (Taiwanese brass cased).

    The other wild card here is also the fact that heavier and slower ammo means more Dwell Time! If I cannot get the 11.5M reliable with 55gr ammo then I will try the 77gr Mk262 clone ammo.

    My FIL has a plain vanilla 11.5C BCM with an FSP. I will function test the Faxon barrel unsuppressed and will try to shoot these uppers together.
    55 grain works. We tinkered with it significantly prior to putting out this model.

  9. #19
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    Let the games begin!

    Barrel weighs 17.10 oz on an old digital food scale. A 7/64 drill bit fit snuggly in the gas port which means its ~0.1094" which matches what the Faxon website specifies (0.110").

    My plan is still to send it to Adco to pin the SLR gas block. The good news is that the delayed release means I am pretty close to getting my stamp for the Trek which will live on this barrel and I will not shoot my titanium 7.62 can on this thing.


  10. #20
    FaxonNathan Guest
    Looks great! Over 50 pre-orders shipped out so you are in great company.

    Thanks for sharing the photo and we look forward to the range report.

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