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Thread: 10.3" pistol/SBR build questions

  1. #11
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    If I were building a 10.3 w/ adj gblock, I'd tune the gas to run on an h2 sprinco blue or a5h2 sprinco green.

    I would also suggest extractor insert with either sprinco 5 coil, bcm enhanced, or colt gold springs. The bcm or sprinco 100% do not need an o ring, never had a colt, so I can't say.

    If you get the gas down extractor tension isn't as big of a deal.

  2. #12
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    Quote Originally Posted by sidewaysil80 View Post
    The DD 10.5" barrel gas port is a whopping .086" and is certainly over gassed. This is to facilitate the function of the lower cost, underpowered "cheap stuff" ammo. The NSWC Crane spec for the mk18 10.3 is .070", that will function reliably both suppressed and unsuppressed and does not require an adjustable gas block.

    Since you are adding an adjustable gas block you can tune it and essentially "decrease" the port size of your DD barrel. With that being said, I would think you still require the extractor upgrade. The actual MK18's called for this modification and they had the proper gas port size. I think even if running the optimal amount of gas, it still alters the characteristics of the bolt function.

    Here is the actual power point that goes over the MK18.
    http://www.dtic.mil/ndia/2003smallarms/john.ppt

    Just out of curiosity, any particular reason you are going with the DD barrel and adj. gas block as opposed to something with a smaller gas port?
    Have you checked a barrel and saw that it was .086? All the reports I have read online have said it is at .082. I have decided to drop the syrac and go with the govnah instead. I'm going to get a dual custom port with .070 and .082(factory) ports. Then when I get the silencer I will just get a new plate.
    Last edited by black22rifle; 03-22-15 at 23:50.
    If there is no enemy within the enemy outside can do us no harm

  3. #13
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    I'm running a DD 10.3" with H Buffer, whatever spring weight comes with a Colt 6920, ARMS #41-BL FSB, and stock Fail Zero BCG.

    Has run fine with a hodge podge of loose ammo around the house. Everything from wolf to PMC to M193 and M855. Never a hiccup in a few hundred rounds since finishing the build a couple of months back.

    I honestly have no idea what the gas port size is, but DD lists it as .750″.
    Last edited by SpecWired; 03-23-15 at 01:05.

  4. #14
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    Quote Originally Posted by SpecWired View Post
    I'm running a DD 10.3" with H Buffer, whatever spring weight comes with a Colt 6920, ARMS #41-BL FSB, and stock Fail Zero BCG.

    Has run fine with a hodge podge of loose ammo around the house. Everything from wolf to PMC to M193 and M855. Never a hiccup in a few hundred rounds since finishing the build a couple of months back.

    I honestly have no idea what the gas port size is, but DD lists it as .750″.

    I think DD is referring to the diameter of the barrel at the port with that figure, not the actual port diameter.

    I'm glad to hear that your rifle runs just fine with an H buffer and a milspec spring though. I'm planning on getting a 5.56 SocomRC 2 when they come out this year and wasn't sure if I would need to make any changes to my rifle. It's a factory DD MK18. I've already bought an H2 just to see. I can't stop buying stuff!!

  5. #15
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    Frickin double click.
    Last edited by SonOfAGunn; 03-23-15 at 12:52. Reason: double

  6. #16
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    Here is a thread that provides some really relevant info.
    https://www.m4carbine.net/showthread...LTOR-A5-on-SBR


    Especially post 41
    https://www.m4carbine.net/showthread...73#post2009973

    Both the 10.5" and 11.5" will need about the same gas port size suppressed, but the 11.5 will allow use of a smaller gas port size unsuppressed.

    This reduces the gap between suppressed and unsuppressed gas drive.

    A low back pressure suppressor will also reduce the difference in gas drive.

    The A5 helps cover the remaining difference.


    Also take the time to read through all 97 pages of this epic thread regarding SBR and suppressor recipes.
    https://www.m4carbine.net/showthread...essed-SBR-Ever
    Last edited by Clint; 03-23-15 at 16:24.
    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

  7. #17
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    Quote Originally Posted by SonOfAGunn View Post
    I think DD is referring to the diameter of the barrel at the port with that figure, not the actual port diameter.

    I'm glad to hear that your rifle runs just fine with an H buffer and a milspec spring though. I'm planning on getting a 5.56 SocomRC 2 when they come out this year and wasn't sure if I would need to make any changes to my rifle. It's a factory DD MK18. I've already bought an H2 just to see. I can't stop buying stuff!!
    Thanks for the info.

    My gun thus far has run well, but I'm might try an H2 and see if it yields any improvements in shootability.
    Listen. Tell. Run Like Hell.

  8. #18
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    Here's something interesting, I just checked the gas port on this DD 10.3 barrel and the gas port came out to .0785" with a #47 drill bit.
    If there is no enemy within the enemy outside can do us no harm

  9. #19
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    Quote Originally Posted by black22rifle View Post
    Here's something interesting, I just checked the gas port on this DD 10.3 barrel and the gas port came out to .0785" with a #47 drill bit.
    When was it made, if you know?

  10. #20
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    The barrel is dated 07/14.
    Last edited by black22rifle; 03-24-15 at 14:41.
    If there is no enemy within the enemy outside can do us no harm

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