Gas tube touching barrel

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  • worthen86ford
    Warrior
    • May 2016
    • 110

    Gas tube touching barrel

    Working on a 10.5 inch 6.5g pistol. Its a cut down anderson barrel. Just put the gas tube in the block, and as i slid the gas block on I noticed that the gas tube is contacting the raised sholder of the barrel just behind the gas block.

    I tried the same set up on a spare unused BCA 5.56 barrel and it does the same thing. All my other builds have been with SS barrels of better quality (cmmg, AA, etc...) and the same shoulder is a smaller diameter that does not interfere. I have an old fsb and without a gas tube appears that it would clear the shoulder if a gas tube was installed.

    I do not think it will affect function but i could imagin a gas tube rupture given enough rounds. Thinking the tube and barrel will rub until the wall is gone on the tube.

    Is this a legit concern? Should i go ahead and turn down the shoulder? I'd rather not cause then i'd need to cerekote or parkerize the machined area. Are some barrels designed to use fsb blocks only? Are fsb gas tubes any different?
  • just_john
    Chieftain
    • Sep 2012
    • 1565

    #2
    Can you add a picture? Would help a lot. tnx

    Comment

    • worthen86ford
      Warrior
      • May 2016
      • 110

      #3


      Comment

      • ricsmall
        Warrior
        • Sep 2014
        • 987

        #4
        I wouldn't think that would be conducive to an accurate rifle. I'd have that shoulder turned down or change gas blocks. Not sure that another gas block will help tho.

        Richard
        Member since 2011, data lost in last hack attack

        Comment

        • A5BLASTER
          Chieftain
          • Mar 2015
          • 6192

          #5
          Yea that looks like a disaster waiting to happen, I see that it's a set screw style gas block maybe a clamp style gas block would set up higher allowing the tube to clear the high spot on the barrel.

          I have a clamp style gas block on my barrel right now if you would take a messurement of yours and I will compare it to mine and see if the clamp style I have holds the gas tube higher then the block you have.

          Comment

          • A5BLASTER
            Chieftain
            • Mar 2015
            • 6192

            #6
            Just looking at the pic you posted and the adjustable block I have on my barrel it looks like my tube would be higher but I haven't messured it yet to see how high it sits off the barrel.

            Comment

            • LRRPF52
              Super Moderator
              • Sep 2014
              • 8569

              #7
              Originally posted by A5BLASTER View Post
              Yea that looks like a disaster waiting to happen, I see that it's a set screw style gas block maybe a clamp style gas block would set up higher allowing the tube to clear the high spot on the barrel.

              I have a clamp style gas block on my barrel right now if you would take a messurement of yours and I will compare it to mine and see if the clamp style I have holds the gas tube higher then the block you have.
              How is it a disaster waiting to happen?

              Maybe not ideal, and probably inconsequential on a 10", but a disaster? I'm not seeing anything approaching disasterous.

              The only thing I wonder about is the gas block tube location being a little low, since I presume the FSB didn't do this.

              If the location is low, what will that do for tube alignment into the carrier key? Will it cause binding, for example?
              Last edited by LRRPF52; 03-03-2017, 06:22 PM.
              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

              • worthen86ford
                Warrior
                • May 2016
                • 110

                #8
                Gas block journal is .749"
                Shoulder where tube is hitting is .981"
                From bottom of gas block ID to bottom of gas tube is ~.865"

                Based on these rough measurements:
                Distance from top of gas block ID to bottom of tube = .116"
                Radial distance from shoulder OD to gas block journal OD = .116"

                So it only interferes by a few thou at most. I think i'm gonna file a shallow channel where its hitting to relieve it. I'll just have to oil the white metal or blue it or coat it idk yet just keep it from corroding too bad

                Comment

                • A5BLASTER
                  Chieftain
                  • Mar 2015
                  • 6192

                  #9
                  Probably a strong word to have used, it's just in my nature with what I do for a living, anytime a tube that has something that runs throw it i.e. gas and can sit and rub on something that creates a place for a rupture and to me that's a disaster.

                  Comment

                  • LRRPF52
                    Super Moderator
                    • Sep 2014
                    • 8569

                    #10
                    Originally posted by A5BLASTER View Post
                    Probably a strong word to have used, it's just in my nature with what I do for a living, anytime a tube that has something that runs throw it i.e. gas and can sit and rub on something that creates a place for a rupture and to me that's a disaster.
                    You would have to run the gun on FULL AUTO mag dumps repeatedly without rest to get a failure of that type, where you exceed the yield of the weakest component.

                    It wouldn't matter if the tube was contacting the barrel in that case anyway.
                    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

                    • worthen86ford
                      Warrior
                      • May 2016
                      • 110

                      #11
                      Originally posted by LRRPF52 View Post
                      How is it a disaster waiting to happen?

                      Maybe not ideal. and probably inconsequential on a 10", but a disaster? I'm not seeing anything approaching disasterous.

                      The only thing I wonder about is the gas block tube location being a little low, since I presume the FSB didn't do this.

                      If the location is low, what will that do for tube alignment into the carrier key? Will it cause binding, for example?
                      If it is abnormally low, it did not cause issues when the block journal was on a mlgs 5.56 barrel. Having said that this is a clgs and something is pushing up on the tube so it might bind up. I dont think it would be too disastrous nor affect my accuracy by any noticeable amount. I figure with this quality of barrel and iron sights it will be wearing, i do not expect any better than 3 moa and with me shooting will probably be more like 6" groups at 100yrds. This is a spare parts build and will compliment my 16" scoped grendel as a backup hunting pistol for east texas with critters inside 75yrds.

                      Comment

                      • sneaky one
                        Chieftain
                        • Mar 2011
                        • 3077

                        #12
                        Go to a local body shop- beg borrow or pay for a small piece of 1500 grit sandpaper- run that back and forth between the 2 items, until you have at Least-.0003 of clearances.

                        That should get you awesome groups at long ranges. And even better at close range- say 20 yds., like I shoot at deer. Let us know your results, please.

                        YES, do some version of a paint type coating to resist rust, & corrosion. I use a LLoyds product called KRYPTONITE, anti corrosive primer.
                        Last edited by sneaky one; 03-05-2017, 02:05 AM.

                        Comment

                        • just_john
                          Chieftain
                          • Sep 2012
                          • 1565

                          #13
                          As close as the gas block is to the shoulder on the barrel, there should be little to no vibration to cause it to rub thru. If there is a concern, it would be more about creating a hot spot in the tube there. As per sneaky, remove just enough metal from the barrel shoulder to eliminate actual contact and you should be good to go. Happy hunting!

                          Comment

                          • worthen86ford
                            Warrior
                            • May 2016
                            • 110

                            #14
                            Since this is a spare parts build, i have decided to take an old fsb and tap it for set screws to use as the gas block and front sight. Gas tube does not interfere this way. For what it's worth, i took a couple of other gas blocks off of some other rifles i have and none of them had this issue. I guess this block is just a little lower profile than most. Idk know what brand it is either.

                            Comment

                            • Texas
                              Chieftain
                              • Jun 2016
                              • 1230

                              #15
                              As long as the gas tube aligns properly with the bolt, the only issue I can see with this is a harmonics change which might slightly affect accuracy. As LRRPF52 said, if you are going FULL AUTO and doing several mag dumps, it coult cause a hot spot in the gas tube which might eventually cause a failure in the gas tube. I dumped 420 rounds through an M4 suppressed in less than 3 minutes and the gas tube did not fail, it set the grip on fire, but the gas tube was still very useable.

                              Comment

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