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Thread: Measuring the barrel gas port size

  1. #11
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    Quote Originally Posted by Magic_Salad0892 View Post
    I take it a digital calliper wouldn't work...
    You can get an "idea," but generally no.



    C4

  2. #12
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    Quote Originally Posted by jmart View Post
    Much better prices on these pin guages.

    Just get 8-10 around the diameter you are trying to measure (e.g., around .062") and go from there. If your largest guage fits in the port, then it's prety obvious you are overgassed, and this should lead you to playing with heavier buffers/spings/carriers, barrel replacement, or a weld up and re-drill job.
    Interesting, so for the range we're talking about they are $2.00 ea and you order them by the piece for the sizes you're looking for? What increments would you buy? 0.0620 through what size at the high end, in what increments? It appears they sell them in 0.0005 increments. I'm assuming you're not suggesting:
    0.0620
    0.0625
    0.0630
    0.0635
    etc.

    but perhaps
    0.0620
    0.0630
    0.0640
    0.0650
    etc.
    ?

  3. #13
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    Quote Originally Posted by C4IGrant View Post
    Feeler gauges are the way.
    Feeler gauges? I thought feeler gauges were flat metal used for measuring gaps?


  4. #14
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    I would also like to hear from people that have measured, or think they have measured, some ports and what kind of size range you've encountered. I've seen posts mentioning down to 0.060 and up to 0.090, which would be a total of 31 pins at .001 increments. I'd hate to buy $60 worth of pins only to find out I need one two sizes smaller, or two sizes larger.

  5. #15
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    I have no way of verifying/vouching but this post has some interesting information.

    http://arizonashooting.com/v3/viewtopic.php?f=8&t=12922

  6. #16
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    Quote Originally Posted by rob_s View Post
    Interesting, so for the range we're talking about they are $2.00 ea and you order them by the piece for the sizes you're looking for? What increments would you buy? 0.0620 through what size at the high end, in what increments? It appears they sell them in 0.0005 increments. I'm assuming you're not suggesting:
    0.0620
    0.0625
    0.0630
    0.0635
    etc.

    but perhaps
    0.0620
    0.0630
    0.0640
    0.0650
    etc.
    ?
    The latter. And I'd probably buy them in .002" steps, e.g., .062, .064, .066, .068, .070, .072. I seriously doubt .001 makes that much of a difference, but it may be worth $25 to find out if your port is .010" or more over spec.

    And regarding my earlier point, I'm in agreement with you with respect to brakes and other add-ons. But if you are having trouble with functioning or you're engaging in a build, knowing your gas port diameter is a good number to have so you can go in the right direction.

    I would suggest you probably wouldn't be well served if you are thinking of purchasing a Colt or BCM, but if you are looking at a build and buying things pieces at a time, it would be useful to know what you're dealing with WRT to the port, then you can make infomed decisions about springs and buffers. And for an alreday assembled carbine, it also can help isolate functioning issues and lead to to the right corrective actions.

    Alternatively, just assemble from whatever parts you have on hand or shoot what you bought with whatever ammo you bought and then maybe subject yourself to having to swap out springs, buffers and mags until you find a combo that works. That can work as well, it's just time consuming, funds consuming and PITA challenging.
    Last edited by jmart; 08-31-11 at 10:14.

  7. #17
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    Quote Originally Posted by rob_s View Post
    While I am generally opposed to the amount of attention paid to this level of minutiae
    Just curious as to why the opposition? This forum has plenty of threads discussing the finer points of H vs. H2 buffers, ejector springs and O-rings, and so on.

    Is the resistance because the gas port dimension is thought to be proprietary knowledge? I'll admit that properly* measuring a gas port is harder to do than reading the H stamp on a buffer, but it's not industrial espionage or "reverse engineering" (as some industry professionals on this board have whined). You own the rifle. It's your bitch. Measuring it ain't no crime. If the manufacturer didn't want you to measure it, they made a big mistake in the first place by selling it.



    * Use pin gages, not calipers. Though a numbered drill index can give you a rough idea.
    Oh no, not another lube thread! Read this first: Lubrication 101.

  8. #18
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    Quote Originally Posted by jmart View Post
    The latter. And I'd probably buy them in .002" steps, e.g., .062, .064, .066, .068, .070, .072. I seriously doubt .001 makes that much of a difference, but it may be worth $25 to find out if your port is .010" or more over spec.

    And regarding my earlier point, I'm in agreement with you with respect to brakes and other add-ons. But if you are having trouble with functioning or you're engaging in a build, knowing your gas port diameter is a good number to have so you can go in the right direction.

    I would suggest you probably wouldn't be well served if you are thinking of purchasing a Colt or BCM, but if you are looking at a build and buying things pieces at a time, it would be useful to know what you're dealing with WRT to the port, then you can make infomed decisions about springs and buffers. And for an alreday assembled carbine, it also can help isolate functioning issues and lead to to the right corrective actions.

    Alternatively, just assemble from whatever parts you have on hand or shoot what you bought with whatever ammo you bought and then maybe subject yourself to having to swap out springs, buffers and mags until you find a combo that works. That can work as well, it's just time consuming, funds consuming and PITA challenging.
    We're not far off from being on the same page then. I just sometimes think that with some of these discussions we're putting the cart before the horse and a lot of people get confused and start to think that it really matters. As we also found in one thread, most people wouldn't know what the number means even if they have it, and even if it is accurate.

    What I'm hoping to do with this thread is get some accountability in these discussions since apparently we are going to have them whether I like it or not. That is why I propose that people tossing numbers around either claim those numbers as their own and tell us how they measured them, or link to the source of the information they got if they are just regurgitating. and also why I'm willing to spend a few dollars to get the gauges to measure some ports myself because they I'll KNOW I did it right and not rely on a guy jamming Home Depot drill bits into the hole in his barrel and calling it accurate to 0.001 (or 0.002 as the case may be).

  9. #19
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    Quote Originally Posted by kartoffel View Post
    Just curious as to why the opposition? This forum has plenty of threads discussing the finer points of H vs. H2 buffers, ejector springs and O-rings, and so on.
    Because it's generally minutia that doesn't matter, and it misleads newer shooters into thinking that it does matter. As mentioned there was already one thread here I can recall where someone was trying to find out his gas port size with absolutely NO idea what to do with the information if he had it.


    Which doesn't let the brake/buffer/spring/o-ring people off the hook either in terms of useless minutiae.

  10. #20
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    Quote Originally Posted by rob_s View Post
    Which doesn't let the brake/buffer/spring/o-ring people off the hook either in terms of useless minutiae.
    +1 to that!
    Oh no, not another lube thread! Read this first: Lubrication 101.

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