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Thread: NSR 13.5 rail and BCM 16" upper. Something is crooked.

  1. #1
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    NSR 13.5 rail and BCM 16" upper. Something is crooked.

    Today I assembled my new 16" LW BCM upper with a NSR 13.5 rail. Something is off center.

    I can't tell if it's the rail or the barrel. When I look at it from the end, and from the top or bottom, it is definitely closer to the left side of the rail by several millimeters. It's enough that I noticed it almost immediately after finishing the build.

    I am leaning toward the rail being the culprit, because when looking down the barrel from the rear of the upper, I can't see any sort of bias to the left at all. It appears perfectly straight. I did notice, however that the barrel was VERY hard to remove, much more so than previous uppers.

    Two questions:

    -How can I narrow the problem down to the barrel/receiver or the rail?

    -Is this something that can be caused by improper torque on the barrel nut?

  2. #2
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    What torque spec did you use? What upper are you using? Does it have the index pin?

    I would possibly remove the rail, slide it back into place and then use an optic mount like a TA-51 and clamp it to the upper and rail while you tighten the screws. down.


    Quote Originally Posted by 1911-A1 View Post
    Today I assembled my new 16" LW BCM upper with a NSR 13.5 rail. Something is off center.

    I can't tell if it's the rail or the barrel. When I look at it from the end, and from the top or bottom, it is definitely closer to the left side of the rail by several millimeters. It's enough that I noticed it almost immediately after finishing the build.

    I am leaning toward the rail being the culprit, because when looking down the barrel from the rear of the upper, I can't see any sort of bias to the left at all. It appears perfectly straight. I did notice, however that the barrel was VERY hard to remove, much more so than previous uppers.

    Two questions:

    -How can I narrow the problem down to the barrel/receiver or the rail?

    -Is this something that can be caused by improper torque on the barrel nut?



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  3. #3
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    Quote Originally Posted by Iraqgunz View Post
    What torque spec did you use? What upper are you using? Does it have the index pin?

    I would possibly remove the rail, slide it back into place and then use an optic mount like a TA-51 and clamp it to the upper and rail while you tighten the screws. down.
    Sorry I should have specified that the rail is "clocked" perfectly to the upper, but the end of the barrel is horizontally biased towards the left side of the rail.

    I used the proper torque as indicated in the rail installation instructions. 40ft-lbs three times followed by final torque of a max of 80 ft-lbs. There is an index pin, but it doesn't specify how it is used. I am using a standard bcm upper receiver.

  4. #4
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    Could you post some pics?

    "Addressing the problem of shootings by ban or confiscation of non-criminal's guns is like addressing the problem of rape by chopping off the Johnson of everyone who DIDN't rape anyone while not only leaving the rapists' equipment intact, but giving them free viagra to boot." --Me

  5. #5
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    Re: NSR 13.5 rail and BCM 16" upper. Something is crooked.

    I wrote about this a while ago.

    Basically, the culprit is most likely your barrel extension or upper receiver.

    The dimensions of those areas are not required by spec to be at the level of straightness that you need to ensure that your barrel will be perfectly centered inside a floating tube.

    Still, it is not a functional issue, and if you can't get over it you can fix it with some work.


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  6. #6
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    Quote Originally Posted by Failure2Stop View Post
    I wrote about this a while ago.

    Basically, the culprit is most likely your barrel extension or upper receiver.

    The dimensions of those areas are not required by spec to be at the level of straightness that you need to ensure that your barrel will be perfectly centered inside a floating tube.

    Still, it is not a functional issue, and if you can't get over it you can fix it with some work.


    Typos brought to you via Tapatalk and autocorrect.
    Is this where those receiver truing tools come in?

  7. #7
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    Check to see if your gas block is touching the inside of the rail, or any rail additions you may have added.

    I had a similar issue and found the gas block up against a mounted rail backing piece.
    Maker of: "The TALON" Pocket Video Camera Mount.

  8. #8
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    I too couldn't tell if my BCM 14.5" middy had a crooked barrel, barrel nut or if the 12" C4 rails were just misaligned.

    I solved it by buying a VTAC ALPHA 13" rail, and installing that...it was worse than the C4s.

    I just returned it to BCM, so hopefully it'll get fixed. With a pinned muzzle device, it's important to me that whatever future rails I put on it (that work with a standard barrel nut) align well.
    --

    If it's the UPPER, it would seem the barrel is also crooked right, or is it generally just the barrel nut?

    (My post was deleted on TOS for fear of upsetting a sponsor...even though I prefaced it by saying I wouldn't name the manufacturer.)

  9. #9
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    There is an index pin, but it doesn't specify how it is used. I am using a standard bcm upper receiver.[/QUOTE]

    the index pin is used with the VLTOR/Noveske upper
    so far to the left i must be right.

  10. #10
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    I had an NSR on my last Colt and didn't use the pin--would have required drilling a hold in the upper. I never had a problem.

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