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Thread: Which gas port size for 14.5 cut to 10.3 for both unsuppressed and suppressed use?

  1. #11
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    Considered the SLR but prefer the simplicity of the Govnah.

    Quote Originally Posted by MistWolf View Post
    My 10.5 has a gas port of .082" and it's just too large. It works well enough unsuppressed with a rifle RE assembly, but it works even better with the SLR AGB. I gave the Govnah a serious look but in the end, the lighter weight and ease of fine tuning of the SLR won out

  2. #12
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    Not sure what Stag was using, want it to work suppressed and unsuppressed (therein lies the problem). I'm having them open it to .073" and see how that works, and am leaning toward using a Govnah.

    Quote Originally Posted by BC98 View Post
    OP,

    The gas port on your Stag barrel is likely fairly large anyway so I doubt that you would need to have it opened up much (if at all) in order to function .223 pressure ammo. For a 10.3" barrel I would honestly start with no more than a .070" port and just see if it runs suppressed. If you're going to be suppressed the majority of the time, then I would suggest starting closer to .060" and working up, if necessary.

  3. #13
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    No, it's unverified. Have seen a lot of people claim this, though, for the Colt 694x 10.3" barrels.

    Contrast this to people who claim to have spoken to sources at Colt who state their MK18 barrels use a .068" gas port. Which would make sense, since .mil uses 5.56 and nonmil and LE often uses .223 instead.

    Quote Originally Posted by H Wyman View Post
    Has this been confirmed by measurement?

  4. #14
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    True, but the majority of what I use is .223, so I want to err on the side of the port being a little bit bigger. Amphibian of MicroMOA sizes the holes in his regulator plates .003" larger than what he recommends for 5.56 if one is using .223, so that is where I came up with how much larger I would want to go than the MK18 spec.

    Another piece of the puzzle, it is widely reported that the newer DD Mk18 barrels use a .078" port, and they are still overgassed for .223, so I don't want to go quite that large of a port.

    Quote Originally Posted by Iraqgunz View Post
    Not sure where you are reading that, but a Crane spec 10.3" barrel with a .071 gas port will work just fine with military ammunition.

  5. #15
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    Copy that. I have a 6920 barrel that I can have chopped, but wanted to use this one first to see how it goes. I can evaluate from there.

    Quote Originally Posted by Iraqgunz View Post
    You are trying to go cheap which usually ends up bad. Get a known quality Colt or BCM barrel with a carbine gas port of .063 and then have it opened up and cut down.

  6. #16
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    As you are probably aware, in WA, individuals can no longer do their own F1 SBR builds at this time due to how BATF is interpreting I594.

    So, until that changes (if ever), individuals to instead go through a manufacturer to make the SBR, do a F2 (or vice-versa), then transfer it back to the individual on a F4.

    You supply RA with the gun and/or parts, they do the mods, and they submit the F2 and F4 to BATFE.

    Quote Originally Posted by JG007 View Post
    Im doing something similar.

    What do you mean "sbr build through rainier arms", do you mean you are buying the parts through them and having them gunsmith/assemble it?

    I have a chf bcm 11.5 and for this next upper want it about 10.7 (handguard+ can, was originally planning on 10.3), I bought parts through them, and got
    their FN chf, rainier mountain, which is a 14.5 I was told had a .068 port so it might be just about right.

  7. #17
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    Not sure why you would open it ti .073, when there is already an established spec. Maybe I am missing something.

    Quote Originally Posted by sff70 View Post
    Not sure what Stag was using, want it to work suppressed and unsuppressed (therein lies the problem). I'm having them open it to .073" and see how that works, and am leaning toward using a Govnah.



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  8. #18
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    Gunz,

    I want it to work with .223 ammo (though not the lower powered of the .223 loads), since I do not typically use 5.56 NATO ammo any more.

    My understanding is that it would be beneficial to open the gas port slightly more than the Crane spec of .070, for unsuppressed use.

    Is that not the case?



    FYI, this particular barrel was from a special run that Stag did, has a 5.56 NATO chamber (though I haven't checked it with a 5.56 chamber reamer) and the rifling is 1/7, so hoping it will stabilize bullets when cut to 10.3, and not have any problems with extraction due to the chamber being tight. I have shot it with M855 and M193 and not had any problems with popped primers.


    Quote Originally Posted by Iraqgunz View Post
    Not sure why you would open it ti .073, when there is already an established spec. Maybe I am missing something.
    Last edited by sff70; 09-01-15 at 09:24.

  9. #19
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    Clint at BRT says the same thing, that .003" is about the port size eqivient to the difference between .223 and 556 chamber pressures for the overall pressure curve in maintaining an appropriate margin of reliability in function. Which is why for mixed use 223/556 unsupressed he recommends a .073" gas block insert when using 10.5" barrels over the crane spec which accounts for exclusively using 556 Nato pressure ammo.

  10. #20
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    Jerrysimons - Thanks, exactly what I wanted to know.

    Quote Originally Posted by jerrysimons View Post
    Clint at BRT says the same thing, that .003" is about the port size eqivient to the difference between .223 and 556 chamber pressures for the overall pressure curve in maintaining an appropriate margin of reliability in function. Which is why for mixed use 223/556 unsupressed he recommends a .073" gas block insert when using 10.5" barrels over the crane spec which accounts for exclusively using 556 Nato pressure ammo.

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