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AR guys: how important is a rattling gas tube?

Discussion in 'Gunsmithing and Repairs' started by 1KPerDay, Jun 7, 2014.

  1. 1KPerDay

    1KPerDay Well-Known Member

    Completing (finally) my first build and the gas tube is perfectly aligned and rattles UNTIL I close the bolt. I removed the bolt from the BCG and I can feel some resistance as the tube enters the gas key. I can't see well enough to tell which way the tube needs to go. I don't really want to take this NIGHTMARE project apart again... the redneck in me says I should be able to tweak/adjust/bend the end of the gas tube in place, but I'm sure there's some really expensive and convoluted way to do it properly...

    Or should I just shoot it and see if it runs? :banghead:
  2. frankenstein406

    frankenstein406 Well-Known Member

    Takes twice as long trying to cut corners is my experience.
  3. 1KPerDay

    1KPerDay Well-Known Member

    Well it seems to run fine... so that's good.
  4. 45_auto

    45_auto Well-Known Member

    I've built dozens of AR15's and always used the Marine Corp Technical Manual (TM 05538C-23) as a reference. All ran perfectly and I've never seen any mention of having a "rattling gas tube'" when the bolt is closed.
  5. 1KPerDay

    1KPerDay Well-Known Member

  6. RussellC

    RussellC Well-Known Member

    Havent had one rattle, and cant really see why it would? Loose at the gas block? If no funky stuff evidencing gas leaking in that area I guess its ok, but what do I know, I just started!:cool:

  7. 1KPerDay

    1KPerDay Well-Known Member

    pinned tight at the gas block, but flexes enough at the other end to rattle against the nut/receiver if you push on it.

    Some say it should rattle with the bolt forward but none of mine do and they all run fine.
  8. RussellC

    RussellC Well-Known Member

    If it runs, I guess its ok. I didnt like the way my gas was pinned, and I freaked out, worried and so forth, all for naught. Like yours, it ran fine.

  9. rcmodel

    rcmodel Member in memoriam

    Just insure the end of the gas tube isn't rubbing off-center in the gas key.

    That will eventually lead to wear, and problems.

  10. 1KPerDay

    1KPerDay Well-Known Member

    How do I check for that? examine the scratches at the bulb at the end of the tube?
  11. rcmodel

    rcmodel Member in memoriam


  12. DT Guy

    DT Guy Well-Known Member

    RC, is there a gun design you DON'T know all the in's and out's of? Seriously, you're encyclopedic in your knowledge, and I, for one, learn a lot from all your posts.

  13. Nappers

    Nappers Well-Known Member

    I've learned a lot from him too!

    He is the Jedi Master, his midichlorians are off the chart!
  14. 1KPerDay

    1KPerDay Well-Known Member

    Ran some more through it yesterday, no malfunctions. The wear on the gas tube bulb appears to be symmetrical as far as I can see.

  15. AlexanderA

    AlexanderA Well-Known Member

    The gas tube shouldn't rattle. Either the hole in the front of the upper receiver is too large, or the outside diameter of the gas tube is too small. (If it rattles, there's a possibility that the tube would be misaligned as it enters the gas key as the bolt carrier closes.) Try another gas tube and see if that solves the problem. Or, turn the barrel nut just slightly to take up the play.
  16. 1KPerDay

    1KPerDay Well-Known Member

  17. amusthj

    amusthj Member

    I'd rather have it rattle than to be too big.

    I just encountered a no-go fit using a Melonited gas tube and Melonited gas key. Apparently the tolerance stack was too great. A replacement stainless gas tube solved my problem.
  18. Owen

    Owen Moderator Emeritus

    interesting. melonite only adds .0001 -.0002" thickness. odd that it would cause a clearance problem. I suspect the parts wre out of tolerance before they were finished.
  19. Arizona_Mike

    Arizona_Mike Well-Known Member

    As long as the tube is not resting against the barrel nut or hole in the receiver, there should be enough play to accommodate a tiny gas key misalignment. If it is significant and your parts are in spec, your gas tube is almost certainly bent. You can straighten them carefully.

    Do you use a dimpling gauge to precisely align your gas block? I have found the gas port on some high quality barrels to be a few degrees off. I have taken a small round file to the top of the barrel nut to get a best compromise alignment before.


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