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Thread: Best general port size for MK18 build

  1. #1
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    Best general port size for MK18 build

    Getting ready to ship my LE6920 off in the next month or so to be cut down to 10.3" for a MK18 build.

    With the exception of the lower, all parts will be the exact same as used on real MK18's.

    My only deviation would be the port size. I know .70 is the correct size for a true clone, but would it be better to run something along the lines of .80-.83 to accept a wider range of ammo?


    Also, as my first SBR, is it a general practice to cut the gas tube down to fit, or do they sell gas tubes for 10.3" barrels?

    Thank you for your time,
    Garrett

  2. #2
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    If you are in that camp, just buy a DD MK18 upper. It has a .82 gas port.

    Most of us run them suppressed and are using cut down barrels or adjustable gas blocks to run in the .70 or lower band.

    Sent from my SM-G930V using Tapatalk

  3. #3
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    I would never recommend a .080-3 port size for any 10.3 barrel. Ever. Run a A5 RE with a A5h2 buffer and colt spring. You will be fine. If you want to run some PMC or something, it probably will still be fine, but run the Standard A5h0 if your concerned and shoot away. Or just run a H buffer in your Carbine RE with car spring and you wont have any problems. Lots of options. Using quality 5.56 ammo, run an H2/3.
    Last edited by Jwknutson17; 02-25-17 at 14:30.
    Philippians 4:13

  4. #4
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    Quote Originally Posted by GarandShooter View Post
    Also, as my first SBR, is it a general practice to cut the gas tube down to fit, or do they sell gas tubes for 10.3" barrels?

    Thank you for your time,
    Garrett
    If your barrel is a carbine, then it is already the right size for the tube. If your barrel is mid length then you should just buy a dd 10,5 barrel that is proper at the factory.

    Personally if it was me id keep the longer barrel as a spare and buy a 10.5 barrel instead. That way its in spec from the ground up.

    But that is me



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    There's no point in chopping the barrel if you're just going to open it up to as big or bigger than what 10.5" barrels are already sold as.

    More cost effective to just sell the barrel and put the money towards the barrel you want.


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  6. #6
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    Quote Originally Posted by jstalford View Post
    There's no point in chopping the barrel if you're just going to open it up to as big or bigger than what 10.5" barrels are already sold as.

    More cost effective to just sell the barrel and put the money towards the barrel you want.


    Sent from my iPhone using Tapatalk
    I disagree. Starting with a colt offers the end user a known quality from which to build from and opening the port up allows selection to specific desired range of performance.

    Plus then it's all colt so win.

  7. #7
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    Best general port size for MK18 build

    Well it just depends on what you're opening it up to...opening the port to .083 is just a waste of a "known quality" barrel.


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  8. #8
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    Quote Originally Posted by jpmuscle View Post
    I disagree. Starting with a colt offers the end user a known quality from which to build from and opening the port up allows selection to specific desired range of performance.

    Plus then it's all colt so win.
    Exactly this, thank you.

    It's a MK18 clone, so a 10.5 would not be nor look correct. Only reason I am okay with changing port size is because it could possible increase usability/function of the gun and cannot be seen. I think I'll just stick to the .70 and see how it goes. Can always go bigger, but not vice versa.

    I was just curious if .8 would allow for a wider range of ammo.

  9. #9
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    I settled on a .073" gas port on mine. I wanted to be able to use a Vltor A5H4 with colt spring and have it function test with Federal 55 gr .223. I would start at .070" and not open it up anymore unless you have a problem. The difference in area/volume between .070" and .073" is 9%, that's a pretty big difference. The difference in area/volume between .070" and .082" is 37%, that's huge.

  10. #10
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    Quote Originally Posted by pezboy View Post
    I settled on a .073" gas port on mine. I wanted to be able to use a Vltor A5H4 with colt spring and have it function test with Federal 55 gr .223. I would start at .070" and not open it up anymore unless you have a problem. The difference in area/volume between .070" and .073" is 9%, that's a pretty big difference. The difference in area/volume between .070" and .082" is 37%, that's huge.
    This is exactly the info I was looking for, thank you!

    On the gas tube, did you cut the factory tube to size or purchase one?

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