Need Advice for .906 Front Gas Block

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  • Franklyn
    Unwashed
    • Oct 2014
    • 2

    Need Advice for .906 Front Gas Block

    Hi, I'm new to the forum and have been a Grendel fan for years.
    I have an AA arms 6.5 Hunter with a Shilen 19.5 in barrel. I want to free float the barrel with the goal of decreasing the group size or at least gain some group consistency. Currently I'm getting about 1.5 moa with 123 SMK and 30.3 gr 748. The groups will string or I'll get an flier in a 5 shot group. I've got a decent trigger and a 3-10 Leopold mil dot. I have t take off the FGB to install the float tube so I would like to upgrade with a clamp on.
    As most of you know, the barrel bulge in this barrel for the FGB is .906 diameter. The only low profile gas block in .906 comes from Triton and is held in place by a set screw and probably blue Loctite. If I'm going to change the current FGB which is taper pinned along with blue Loctite, I would like to install a clamp on FGB. I'm unaware of any manufacturer that makes a .906 diameter low profile clamp on FGB so here's the choices:
    Take off the barrel and reduce the barrel bulge to .750. and then use a .750 FGB. I'm hesitant to do this but would consider it.

    Buy a .936 clamp on FGB and then make a .015 thick cylindrical sleeve(.030 total) with properly located port hole and place it in between the .906 barrel bulge and the .936 clamp on FGB. probably use blue Loctite between the FGB and sleeve. Also place a cut along the sleeve length to allow for the clamping action of the FGB to act on the sleeve.
    I'm planning on using 1020/1026 steel for the sleeve.

    Do you think this sleeve would or would not work? Any other ideas?

    I have a 28" lathe with a 3 jaw chuck and also a knee mill.
    Thanks!
  • Drifter
    Chieftain
    • Mar 2011
    • 1662

    #2
    I would use the Triton set-screw if a low-profile 906 block is desired.

    It's possible that the Triton could be pinned.

    Last edited by Drifter; 10-13-2014, 04:36 AM.
    Drifter

    Comment

    • IceAxe
      Warrior
      • Jan 2014
      • 168

      #3
      You might try backing off on the load. I show the next node at 29.0g for 748 and the 123 SMK, 19.5 inch barrel. Pressure variation at near max load could be the culprit. Just a thought.

      Comment

      • LRRPF52
        Super Moderator
        • Sep 2014
        • 8569

        #4
        Welcome. You can also get one of the popular .875" clamp-on or set screw gas blocks and ream it, then you don't have to modify the barrel.

        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

        • Franklyn
          Unwashed
          • Oct 2014
          • 2

          #5
          Thanks for the replies.
          Regarding the reaming, a 29/32 reamer is .90625 diameter. Do you think this could ream a .875 hole which is not completely surrounded in steel (the clamp is a split ring) to .90625?
          How would you support the .875 split ring clamp gas block to minimize flex while reaming? I'm thinking of using a 4 jaw rotary table on the mill as a possible way of doing this.

          Comment

          • LRRPF52
            Super Moderator
            • Sep 2014
            • 8569

            #6
            If it were mine, I would consider just turning down the gas block journal to .875" with someone who knows how to maintain concentricity/good machinist.
            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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