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Thread: Gas Block Jig Issue

  1. #1
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    Gas Block Jig Issue

    Anyone ever run into issue where you used a gas block set screw jig and then the gas port did not align correctly with the gas block?

  2. #2
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    Can you be a little more specific?

    What is the apparent issue?
    Black River Tactical
    BRT Covert Comps 7.62, 5.56, 6X, 9mm
    BRT OPTIMUM Hammer Forged Chrome Lined Barrels - 11.5", 12.5", 14.5"
    BRT EZTUNE Preset Gas Tubes - CAR, MID
    BRT Bolt Carrier Groups M4A1, M16 CHROME

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    I once did not properly align the second set screw, but the one under the port lined up fine. Luckily I removed the jig and slid the gas block on to be sure the dimples would line up before I went full dimple on it. Put jig back on, made sure both alignment screws were tight, repunched second mark and then dimpled like it should have been. So…. I can see how the second dimple can get out of alignment if not double checking. But I am also the type that blues the dimples before securing the gas block on… I am not sure how it would be possible to not align the dimple under the gas port though.

  4. #4
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    Quote Originally Posted by Clint View Post
    Can you be a little more specific?

    What is the apparent issue?
    I'd like to know how he knows it isn't aligned within reason. It's not like the gas port in the GB is anywhere near as small as the port in the barrel.

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    I don't have any issues.
    GB jigs vary, from eyeballing gas port alignment before tightening jig screws, to jigs like KVP where one set screw tapers into gas port for alignment, but there can still be variances between jig and the GB.

    Some barrel ports are large. I have a 300 that's 105 big.

    I was just curious to know if anyone ever ran into alignment issue even though the jig was used correctly.

  6. #6
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    Quote Originally Posted by GH41 View Post
    I'd like to know how he knows it isn't aligned within reason. It's not like the gas port in the GB is anywhere near as small as the port in the barrel.
    I put a bore scope down the barrel (that has angle mirror) and then inspect the gas port. You can see misalignment if it's there.

    How big are GB ports (the hole in GB)? I have one barrel that's 120 and another that's 105. It's not like putting a 125 GB hole over a 62, etc.

  7. #7
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    Some jigs out there are not machined properly. always pays to check it.
    Attached Images Attached Images

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    I have lots of tools to measure stuff, but trying to get accurate hole center locations of the jig,GB, and bbl is not an ez task. Kinda why I asked my question in 1st post, just trying to get a better understanding of the error frequency. I don't find many posts anywhere saying the GB port and bbl port did not align correctly after using jig xyz, etc.

    On my next set screw dimpling I will verify with bore scope.

  9. #9
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    A jig that requires eye balling defeats the purpose of a jig.

    The index should be a cone point screw into the gas port.
    Quote Originally Posted by DwayneZ View Post
    I don't have any issues.
    GB jigs vary, from eyeballing gas port alignment before tightening jig screws, to jigs like KVP where one set screw tapers into gas port for alignment, but there can still be variances between jig and the GB.

    Some barrel ports are large. I have a 300 that's 105 big.

    I was just curious to know if anyone ever ran into alignment issue even though the jig was used correctly.

    Gas block ports are typically .156-159", the same as the drill diameter for the set screw.

    Quote Originally Posted by DwayneZ View Post
    I put a bore scope down the barrel (that has angle mirror) and then inspect the gas port. You can see misalignment if it's there.

    How big are GB ports (the hole in GB)? I have one barrel that's 120 and another that's 105. It's not like putting a 125 GB hole over a 62, etc.
    Black River Tactical
    BRT Covert Comps 7.62, 5.56, 6X, 9mm
    BRT OPTIMUM Hammer Forged Chrome Lined Barrels - 11.5", 12.5", 14.5"
    BRT EZTUNE Preset Gas Tubes - CAR, MID
    BRT Bolt Carrier Groups M4A1, M16 CHROME

  10. #10
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    Quote Originally Posted by Clint View Post
    A jig that requires eye balling defeats the purpose of a jig.


    Gas block ports are typically .156-159", the same as the drill diameter for the set screw.
    Well, not on a Odin Works GB it's not. The port hole measures in at 124. 125 is a common tool size, but using my ZZ pin set I measure 124. The set screw hole dia is 153.

    So with this GB the 124 needs to be over the 105 of the barrel. That's only 9.5 in any radius direction to be not aligned. On my caliper 10 is a fairly small space, but perhaps big enough to allow a smidge of offset while locking down set screws.

    Some barrels even come with 125 port.

    Hence my original question.

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