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Thread: Gas Block Clearance

  1. #11
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    I would thing a credit card thickness would be appropriate.. (pun intended) but what do i know.. Cheers.. Ron
    Ain't no pockets on a shroud..

  2. #12
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    Quote Originally Posted by AKDoug View Post
    Any end view shots? How tight is the gas block when you slide it on the barrel? The barrel is .750" at the gas block area, right?
    Here is the top and bottom (click the image for bigger size):




    The gas block fits snugly over the barrel and comes off with a little force, but not to the point that tools are required. The barrel is .750 at the gas block (spot on according to my caliper). What's weird is that the gas block measures .742in between 3 and 9 oclock, and .752in between 6 and 12. Is that normal? (I doubt that has anything to do with the rail clearance, it's just intriguing)

  3. #13
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    That looks really close.. I use a brake cylinder hone if the gas block is too tight, so far all that I've had were too tight.. Ron
    Ain't no pockets on a shroud..

  4. #14
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    Quote Originally Posted by Kokopelli View Post
    That looks really close.. I use a brake cylinder hone if the gas block is too tight, so far all that I've had were too tight.. Ron
    The gas block fits fine onto the barrel, it's the barrel / rail alignment that is off.

    Is there a procedure for checking alignment of the barrel? I'll borrow a machinist straight edge from work to inspect it the rail against the, but I don't know what I need to do to make sure the barrel is seated properly.

    This is sitting on a Aero Precision upper receiver, are they known for being quality or could that be the problem?

    edit: Scratch that, I had one in my garage that my friend left a few weeks ago. The rail is level when checked against the top of the receiver. Seems like barrel is not sitting flush. When I was torquing down the barrel nut, the vise block slipped out and the upper receiver took a 3 foot drop onto the floor ( ). It landed on the forward assist, but would the receiver bouncing be enough to offset the barrel? This is a bull barrel and I don't see any marks indicating impact anywhere on the barrel.
    Last edited by netchemica; 06-08-13 at 13:44.

  5. #15
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    I understand.. I was referencing the "out of round" inside diameter of the gas block you mentioned. I saw that it went on OK; just kinds threw that in.

    I thought the issue was the bottom of the gas block impacting the handguard/tube. A good pick of the muzzle that shows the handguard might show something.. Ron

    I think you could just grind this down...

    Last edited by Kokopelli; 06-08-13 at 15:25.
    Ain't no pockets on a shroud..

  6. #16
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    Gas Block Clearance

    The drop shouldn't have done anything serious. I'd grind and move on. A 1/16 should be enough with a barrel that stiff.


    Sent from my iPhone on tapatalk

  7. #17
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    Quote Originally Posted by rvb View Post
    I've been trying to get an answer to this recently myself due to a troy/vtac rail that isn't sitting centered around the barrel. A highpower high-master i spoke with suggested that a folded over dollar bill was enough clearance. Im looking forward to hearing other inputs.

    -rvb
    A dollar bill is the rule of thumb used for bolt actions when free floating around the stock.
    -Thomas

    Member, ISRA; Life Member, NRA; USCCA Certified Instructor; NRA Certified Instructor, AGI Certified Gunsmith, Illinois Concealed Carry Instructor
    www.alphakoncepts.com www.gunrights4illinois.com

  8. #18
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    Quote Originally Posted by netchemica View Post
    Here is the top and bottom (click the image for bigger size):




    The gas block fits snugly over the barrel and comes off with a little force, but not to the point that tools are required. The barrel is .750 at the gas block (spot on according to my caliper). What's weird is that the gas block measures .742in between 3 and 9 oclock, and .752in between 6 and 12. Is that normal? (I doubt that has anything to do with the rail clearance, it's just intriguing)
    Top looks fine, bottom looks TIGHT. I'd consider milling down a few thousands from the bottom of the gas block on my milling machine.
    -Thomas

    Member, ISRA; Life Member, NRA; USCCA Certified Instructor; NRA Certified Instructor, AGI Certified Gunsmith, Illinois Concealed Carry Instructor
    www.alphakoncepts.com www.gunrights4illinois.com

  9. #19
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    Re: Gas Block Clearance

    Dammit, I was getting ready to order a CMR, but I keep seeing fitment issues. Does anyone have Vltor & BCM gas blocks sitting around that can measure them for overall height? I'd order a Centurion gas block, but those are no where to be found.

  10. #20
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    Have you confirmed that the CMR is aligned properly? Perhaps loosening the clamping screws and see if you could vertically realign the CMR. I imagine a couple thou shift at the mounting point would give you enough clearance at the gas block.

    You could put a straight edge along the top rail and see if the CMR is tilted upwards.

    Before grinding any more, I would rather confirm barrel and rail alignment.
    Last edited by crosseyedshooter; 06-10-13 at 16:30.

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