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Thread: Measuring the barrel gas port size

  1. #81
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    Daniel Defense 14.5 Mid Length Gas Port Size .076

    A #48 drill bit fits nice and snug in my new barrel.


  2. #82
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    Quote Originally Posted by archad View Post
    A #48 drill bit fits nice and snug in my new barrel.

    Looks like the #48 is .0760".

    See the link below for drill bit sizes.

    http://www.carbidedepot.com/formulas-drillsize.htm

  3. #83
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    BCM 14.5 ML/LW Gas Port

    I just removed the FSB off my BCM. I used the same drill bit #48 which is .0760" fits just like it did in the DD barrel. Sorry crappy pic.


  4. #84
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    Quote Originally Posted by rob_s View Post
    I ordered 31 of the McMaster pins, individually. 0.060 through 0.080 in 0.001 increments.
    Rob, are you satisfied with this selection? I assume you ordered 21 instead of 31?

  5. #85
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    Folks, unless you are using gage pins for a living, an import brand is "good enough". They're to size and simply don't have NIST traceability and typically class ZZ. Gold standard would be a set made by Vermont or Meyer, or Starrett. If you have a bottomless wallet, buy some Deltronic class X in 0.0001" plus and minus increments.

    These barrel manufacturers in all likelihood are using reamers in some 0.001" increment. If you're going to start fretting over pin brands, better ditch the import calipers and micrometers I see in photos.

    Be careful not to bottom out the pins when inserting into the hole. You risk dinging up the lands on the opposite side of the bore.
    “The practical success of an idea, irrespective of its inherent merit, is dependent on the attitude of the contemporaries." Nikola Tesla

  6. #86
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    Quote Originally Posted by Achpamsin View Post
    Rob, are you satisfied with this selection? I assume you ordered 21 instead of 31?
    I wound up with pins, I think, 0.060 through 0.100 in 0.001 increments.

    Were I doing it over again I'd probably just pony up for this set, which comes with a box.

    http://www.mcmaster.com/#catalog/118/2289/=g782cs

  7. #87
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    Quote Originally Posted by archad View Post
    A #48 drill bit fits nice and snug in my new barrel.

    That's off a tiny bit from what DD says their port size is for that barrel but probably not enough to matter. I can't help but wonder, however, what it would gauge at vs. just sticking a drill bit in.

  8. #88
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    Quote Originally Posted by rob_s View Post
    That's off a tiny bit from what DD says their port size is for that barrel but probably not enough to matter. I can't help but wonder, however, what it would gauge at vs. just sticking a drill bit in.
    One thing I've been wondering is how are these gas ports made if there are no drill bits the actual size of the port?

    I hate to imagine that bubba gunsmith is just using a smaller one and wiggling it around to open up the hole to the needed size.

    ETA - Okay I just read the post above by Cesiumsponge regarding the incremental reamer. That makes sense to me.
    Last edited by Yojimbo; 02-11-12 at 09:05.

  9. #89
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    Quote Originally Posted by Yojimbo View Post
    One thing I've been wondering is how are these gas ports made if there are no drill bits the actual size of the port?

    I hate to imagine that bubba gunsmith is just using a smaller one and wiggling it around to open up the hole to the needed size.
    I have no doubt that an outfit the size of DD or Colt can order a reamer in the specific size that they need, and that the army of engineers at Colt know how to calculate what they will need prior to ordering.

    I suspect that for most, however, it's a matter of trial and error. Which is fine, depending on just how much trial to reduce the amount of error.

  10. #90
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    The drill felt the same in the both barrels. Maybe its off a .001" or two. The DD barrel gas port has more a chamfer. The BCM is more like a straight 90 degree if that makes sense. I guess to be exact I should had some pin gauges. Anyway my BCM 14.5 middy shoots real smooth and I expect the DD shoot smooth and maybe more accurate since it CHF.
    Last edited by archad; 02-11-12 at 09:17. Reason: typo

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