gas block question

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  • Dr. Lee
    Bloodstained
    • Sep 2014
    • 68

    gas block question

    What is the correct way to install a gas block so that it is vertical and that the gas port hole lines up with the hole in the block.
    I am looking to replace a picatinny gas block with a low profile block.
    thanks,
    Dr.
  • LRRPF52
    Super Moderator
    • Sep 2014
    • 8569

    #2
    There are many ways to approach this. Do I focus on a perfect TDC, or acceptable port alignment, but with optimal gas tube to carrier key interface?

    I lean to the latter, which is really almost imperceptible when looking at deviation from port alignment between the barrel port and block port. This is one of the most over-looked, yet critical assembly points on the AR15: gas tube to carrier key alignment. If the carrier key clips the tube, you will have accuracy, then reliability problems that will manifest as short-stroking.

    Measure your port locations from the barrel shoulder to center of the gas port.

    Then measure your port location from the rear of the block to the center of the port inside the block. I use my calipers as a protrusion gauge in this effort, looking through the bottom of the gas block set screw hole or seam if it's a clamp-on type.

    Not all barrels are shouldered to the same datum when looking at the ports, because of the old era handguard cap space that needed to be present. Since we basically free-float most of the guns nowadays, there isn't a need for the offset shoulder, especially with the 6.5 Grendel.
    NRA Basic, Pistol, Rifle, Shotgun, RSO

    CCW, CQM, DM, Long Range Rifle Instructor

    6.5 Grendel Reloading Handbooks & chamber brushes can be found here:

    www.AR15buildbox.com

    Comment

    • Eodman
      Unwashed
      • Jan 2015
      • 6

      #3
      I used to install the gas block also measuring the port hole and bbl hole. It would take some time to get it right. When I built my 6.5 I did it this way. Everything looked good. Then I used my bore scope and found That I was off center. I backed off the screws holding the block on and used the bore scope to line up the holes with each other. I know most people don't have access to a bore scope but if you can borrow one it sure makes the job easy.

      Comment

      • montana
        Chieftain
        • Jun 2011
        • 3209

        #4
        LRRPF52 is right on the mark. I will draw a center line from the center of the barrel gas port to the barrel shoulder with a fine pencil using a straight edge. I will do the same with the gas block and mark the center of the gas block face compared to the center of the gas block port.The gas block port is always bigger than the barrel port and I will be able to see how much adjustment I use for the gas tube and still have aligned port holes. I will then use the right feeler gauge width to snug the gas block face to the barrel shoulder for an exact fit if needed. When the marks are aligned I will tighten just enough for a good hold so I can check my gas tube to gas key fit and adjust if needed. When all is good I will then tighten the gas block screws with red loctite. When all is good I can erase the pencil marks.

        Comment

        • LRRPF52
          Super Moderator
          • Sep 2014
          • 8569

          #5
          What I have seen over the years is that the RLGS is the hardest to find good alignment with the carrier key, since the longer tube is more flexible.

          The MLGS seems to be the sweet spot, between the RLGS and the CLGS, with the CLGS of course being very stiff.

          There is a tool to bend the gas tube into more optimal alignment available, if one were to choose that method of addressing alignment of the carrier key and tube.
          NRA Basic, Pistol, Rifle, Shotgun, RSO

          CCW, CQM, DM, Long Range Rifle Instructor

          6.5 Grendel Reloading Handbooks & chamber brushes can be found here:

          www.AR15buildbox.com

          Comment

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