Effects of a misaligned gas port??

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts
  • cb4017
    Warrior
    • Dec 2016
    • 183

    Effects of a misaligned gas port??

    To make a long story short, I have come to the realization that the gas port on my custom barrel does not seem to be aligned with the barrel extension locating pin. To get the gun to run 100% I have to fudge the gas block sideways a bit. That obviously means my gas tube is not centered in the receiver and drags on the gas key.

    I figure that can't be good for accuracy. Is there a fix? Trying to decide if I want to live with it or contact the shop I bought the barrel from. The barrel shoots ok but is not the tack driver I expected.

    Thanks for any input.
    Cliff
    USN Ret., FPD Ret.

    Dues Vult
  • Klem
    Chieftain
    • Aug 2013
    • 3508

    #2
    I would take it back. If your gas tube is not exactly lined-up with the key there will be problems, if not now then certainly down the track when it's too late to take it back.

    If the barrel was a tack driver then I would mount the gas tube to be absolutely square with the carrier and see if there's enough gas to work the system reliably. But in your case it's an average barrel so the answer is clear.

    Comment

    • LRRPF52
      Super Moderator
      • Sep 2014
      • 8569

      #3
      Many times, the diameter of the gas block hole is large enough to still cover the port hole as long as they are aligned on the longitudinal axis (back-to-front).

      The port really needs to be way off of TDC (Top Dead Center) for the gas block port not to cover it.

      What does your gas port shadow look like when the block is aligned TDC?

      If you get a partial occlusion of the gas port, depending on the size of the port, gas system length, and ammo used, it might short stroke.

      It also might run smoother than normal, or make minimal-to-no difference.
      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

      • Lastrites
        Warrior
        • Apr 2017
        • 678

        #4
        Cb you mentioned "custom" barrel and with that I would reach out to the custom maker of said barrel to make it right.

        Comment

        • cb4017
          Warrior
          • Dec 2016
          • 183

          #5
          The issue I was having is it would not lock the bolt back with loads using XBR or AR-Comp. It would with CFE or Hornady factory loads. I figured it was slightly under-gassed. When I dismantled the upper to bed the barrel I noticed a pretty good shadow at the gas port and I assumed things were not lined up. I was very anal when I put the upper back together and it seems to running fine with any loads. AR-Comp looks like it has some potential in this barrel. Here is my first 5 rd group with it. From the prone and with my 64 year old eyes I'll take it.
          Attached Files
          Cliff
          USN Ret., FPD Ret.

          Dues Vult

          Comment

          • LRRPF52
            Super Moderator
            • Sep 2014
            • 8569

            #6
            AR-Comp and 8208XBR are powders that burn faster and don't hit the gas port with as much pressure as ball powders like CFE223 and Hornady's canister powder.

            If 8208XBR and AR-Comp aren't running the gas system, you have some kind of occlusion I suspect.

            Any pics of the carbon shadow at the port?

            The AR15 was actually engineered around powders like 8208XBR (IMR8208M was one of them, along with some other tiny stick powders).

            When the Army Ordnance Board switched over to ball propellant without consulting Colt, Stoner, or anyone from the design team, and went to ball powders, the port pressure skyrocketed, causing cyclic rate increase from the optimum window of 750-850rpm, to 950-1150rpm.

            At that time, the Colt Model 601 and 602 had the Edgewater spring guide, which was really a Browning A5-type recoil system design with conical stacks inside of it and a floating head. One of the fixes for the AR15 to counteract the increased cyclic rate was to use a much heavier buffer with an aluminum body and reciprocating weights with pads in between them inside of the buffer, to act as a rate reducer and dead-blow cascading hammer for countering carrier bounce in Automatic mode.





            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

            • Kswhitetails
              Chieftain
              • Oct 2016
              • 1914

              #7
              Originally posted by LRRPF52 View Post
              AR-Comp and 8208XBR are powders that burn faster and don't hit the gas port with as much pressure as ball powders like CFE223 and Hornady's canister powder.

              If 8208XBR and AR-Comp aren't running the gas system, you have some kind of occlusion I suspect.

              Any pics of the carbon shadow at the port?

              The AR15 was actually engineered around powders like 8208XBR (IMR8208M was one of them, along with some other tiny stick powders).

              When the Army Ordnance Board switched over to ball propellant without consulting Colt, Stoner, or anyone from the design team, and went to ball powders, the port pressure skyrocketed, causing cyclic rate increase from the optimum window of 750-850rpm, to 950-1150rpm.

              At that time, the Colt Model 601 and 602 had the Edgewater spring guide, which was really a Browning A5-type recoil system design with conical stacks inside of it and a floating head. One of the fixes for the AR15 to counteract the increased cyclic rate was to use a much heavier buffer with an aluminum body and reciprocating weights with pads in between them inside of the buffer, to act as a rate reducer and dead-blow cascading hammer for countering carrier bounce in Automatic mode.





              Interesting that you bring this up, Dad and I were discussing this very topic last night, that there were failures in the original M16 (due more in ammunition changes than to the design and construction of the rifle, though either way, it was because the weapon was expected to perform outside it's intended design...) after discussing the thread of a broken extractor... hmmm.
              Nothing kills the incentive of men faster than a healthy sense of entitlement. Nothing kills entitlement faster than a healthy sense of achievement.

              Comment

              • Double Naught Spy
                Chieftain
                • Sep 2013
                • 2560

                #8
                Originally posted by cb4017 View Post
                To make a long story short, I have come to the realization that the gas port on my custom barrel does not seem to be aligned with the barrel extension locating pin. To get the gun to run 100% I have to fudge the gas block sideways a bit. That obviously means my gas tube is not centered in the receiver and drags on the gas key.

                I figure that can't be good for accuracy. Is there a fix? Trying to decide if I want to live with it or contact the shop I bought the barrel from. The barrel shoots ok but is not the tack driver I expected.

                Thanks for any input.
                Custom mismade barrel? Send it back!
                Kill a hog. Save the planet.
                My videos - https://www.youtube.com/user/HornHillRange

                Comment

                Working...
                X