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Thread: Success with getting 9" Barrels to run

  1. #11
    XCR Guru Sean K.'s Avatar
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    Re: Success with getting 9" Barrels to run

    Quote Originally Posted by WatchoutforStobor View Post
    Quote Originally Posted by Sean K. View Post
    So, on your 5.56.....the bbl port was less than 5/64"....which is .078125". Even if you're measuring with just a drill bit and not a precise gauge pin set....that tells me the port was WAAY off to begin with. The 9" 5.56 PDW bbl was supposed to have a factory .086" port.

    I'm going to make some notes here just for ease of future reference for myself if I do size up some of my ports. I have a machinist drill bit set so everything's in decimals.

    9/64=.140625" (5.56 gas block and #4 dial position)

    3/32=.09375" (5.56 bbl port and #3 dial position)

    5/64=.078125 (5.56 #2 dial position)

    1/16=.0625" (5.56 #1 dial position)

    So essentially, the smallest 'port' the gas goes through (with the gas set on 4) in your gun is the bbl port at .09375" .

    Flow through should be the same on 3, assuming (and this is a big ASSumption) that your gas block lines up PERFECTLY with your bbl port (none of mine have but they are all close enough to work). It's only when you get down to setting 2 or 1 that you run into restriction.

    Interesting....Thanks much for the info and exact sizes you're using. I'd like to tinker with mine some more, but at this point I'm out of money to buy ammo for the experiment.

    Sean



    Sean, thanks for the info. You don't happen to have the specs for the 16" 5.56 barrel and gas plug?






    I posted the specs for the 16" in the past....I KNOW the bbl port is .070"....but I'm not sure on the dials. I *think* I was incorrect earlier about the gas block size. I think mine was .128" and it was supposed to be .136" IIRC. I'll go back and edit the other post. I need to go searching for the other info....I just can't remember what thread I posted it all in.

    Sean

    ***EDIT*** These are the specs I was given by RA.

    16" 5.56 rifles should have a .070" bbl gas port and a .136" gas block port. The largest #4 gas dial port is .125".

    9" 5.56 bbls should have a .086" bbl gas port.....gas block port is still .136" and #4 dial port is .125".
    "Necessity is the plea for every infringement of human liberty. It is the argument of tyrants; the creed of slaves."-William Pitt the Younger

  2. #12
    Super Moderator Underground's Avatar
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    Re: Success with getting 9" Barrels to run

    Do you need to do anything special to deburr the hole if you drill out the gas port in the barrel?



    That guy, he said I should be oblong and have my knees removed. But I don't trust him, he plays the banjo.

  3. #13
    XCR Guru Sean K.'s Avatar
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    Re: Success with getting 9" Barrels to run

    Quote Originally Posted by Underground View Post
    Do you need to do anything special to deburr the hole if you drill out the gas port in the barrel?
    I didn't......but I also checked for drill flashing and looked down the bbl to make sure there wasn't any drill flashing hanging down in the path of the bullet. If you use a good, sharp bit, it shouldn't be an issue....but if it is, I'd probably say try and knock it down or out with a brush, then wooden dowel,.....or cleaning rod as a last resort.


    HTH,
    Sean
    "Necessity is the plea for every infringement of human liberty. It is the argument of tyrants; the creed of slaves."-William Pitt the Younger

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  5. #14
    XCR Guru aziator's Avatar
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    Re: Success with getting 9" Barrels to run

    Yeah, I didn't do anything special on the barrel, didn't have any burrs on it.

    The gas dial seemed to have a couple small ones, I just took a drill bit that was slightly smaller than the ID of the entire assembly and cleaned it all out.

    I think I will take pics of the entire process and post them up, might make life easier for someone.
    Don't confuse enthusiasm for competence

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  6. #15
    DSM
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    Re: Success with getting 9" Barrels to run

    FWIW, speaking with a fellow that builds service rifles for competition he used to drill the gas port with a lead slug run down to the appropriate location. After that started to be a real PITA he just said, "oh well" and then shot out whatever burr was left. He hasn't experienced any issues.
    When have any of our plans ever actually worked? We plan, we get there, all hell breaks loose.

  7. #16
    XCR Guru Sean K.'s Avatar
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    Re: Success with getting 9" Barrels to run

    I just checked my new 9.5" PDW bbl....

    I don't have access to the gauge pin set anymore, but the drill size that fit the bbl port was .078".....it's supposed to be .086". I drilled it to .093" and opened both the gas blocks (my 10.5" and 9.5") to .140" from .136". I'm getting ready to open the dials on both the 10.5" and the 9.5".

    Hopefully, I'll be able to do a small amount of testing this week and tell you guys how it goes.

    Sean
    "Necessity is the plea for every infringement of human liberty. It is the argument of tyrants; the creed of slaves."-William Pitt the Younger

  8. #17
    Super Moderator Underground's Avatar
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    Re: Success with getting 9" Barrels to run

    I'll be interested to know how that works for you since I plan on getting a 9" 5.56 barrel soon.



    That guy, he said I should be oblong and have my knees removed. But I don't trust him, he plays the banjo.

  9. #18
    DSM
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    Re: Success with getting 9" Barrels to run

    I think I recall saying Terra saying that the #4 setting was identical on all gas dials.
    When have any of our plans ever actually worked? We plan, we get there, all hell breaks loose.

  10. #19
    XCR Guru aziator's Avatar
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    Re: Success with getting 9" Barrels to run

    Quote Originally Posted by Underground View Post
    I'll be interested to know how that works for you since I plan on getting a 9" 5.56 barrel soon.
    It should work just fine with these mods. I need to get out and shoot mine more but I am busy building a bumper for my truck.
    Don't confuse enthusiasm for competence

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  11. #20
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    Re: Success with getting 9" Barrels to run

    Quote Originally Posted by aziator View Post
    Quote Originally Posted by Underground View Post
    I'll be interested to know how that works for you since I plan on getting a 9" 5.56 barrel soon.
    It should work just fine with these mods. I need to get out and shoot mine more but I am busy building a bumper for my truck.
    Railroad tie not enough for you?



    That guy, he said I should be oblong and have my knees removed. But I don't trust him, he plays the banjo.

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