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Thread: Can't get a good barrel nut alignment.

  1. #1
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    Can't get a good barrel nut alignment.

    I was installing my MI rail and noticed that the only way to align my barrel nut was to either under torque or over torque. When I get to 30ft-lbs, one of the notches is covering the opening for the gas tube. The wrench clicks for 80ft-lbs before I'm able to move it far enough out of the way to make it usable.

    Anything I can do about this? It's a BCM lightweight 16" barrel on a BCM upper receiver.

  2. #2
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    There are a couple of different ways do "fix" this issue. Well three actually.

    1) Do the "torque and release" method whereby you torque (never exceeding your target torque value) and then release it as many times as is necessary till you get alignment.

    2) Barrel Nut shims... good idea... hard to find parts.. I make my own.

    3) Sanding/filing/machining a few thousandths from the barrel extension hole. (Do NOT do this unless you can do the math! It's VERY easy to remove too much material!)

    Have a NICE day,

    TJ
    Quote Originally Posted by markm View Post
    But you should have enough mags that you don't need to see a grief councelor if you destroy or damage one.

  3. #3
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    Moly grease on the threads and the above mentioned torque/release/repeat. Also try a different barrel nut.

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    I had this exact problem with my NSR barrel nut. I had a long way to go in order to index the barrel nut properly while maintaining torque range and was suprised the torque and release method worked. I thought I was going to need a new barrel nut. I used a good amount of moly grease on the threads and a enough on the barrel bushing so the barrel slides easily into the upper receiver.

  5. #5
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    As above, in my order of preference:

    1) torque and release and torque again (you were already using grease to start with, right?)

    2) if it's a GI nut or you otherwise have spares, try a different nut. Generally not an option with proprietary nuts for free float forearms, though you can always call up the maker and they may send you another nut for free or cheap to see if it torques more easily.

    3) I'm not a machinist and have never seen shims offered for sale. Great idea, wish someone would offer them, haven't seen it. If you have the ability to make them, try it.

    4) Sand the front of the receiver very lightly. This should fix it (as a last resort) and I have used this once with installing a proprietary nut that had the same problem you describe - not indexing in the 30 to 80 ft-lb range. It works. Go slow, check often. If you're trying to do a precision build you would want the receiver front perfectly perpendicular to the bore, which probably won't happen if sanding by hand.

    5) Say screw it to the indexing thing, choose one of the newer monolithic style designs (VLTOR VIS, AeroPrecision COP and MEGA KMK) with a nut that doesn't have teeth and doesn't require indexing, it just torques to a stated value, typically in the 45-55 ft-lbs range, and you're done.
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  6. #6
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    The only time I have ever seen a shim on a barrel was a factory built Colt 6540

  7. #7
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    Quote Originally Posted by netchemica View Post
    I was installing my MI rail and noticed that the only way to align my barrel nut was to either under torque or over torque. When I get to 30ft-lbs, one of the notches is covering the opening for the gas tube. The wrench clicks for 80ft-lbs before I'm able to move it far enough out of the way to make it usable.

    Anything I can do about this? It's a BCM lightweight 16" barrel on a BCM upper receiver.
    I find this extremely difficult to believe. Perhaps your wrench is out of calibration? It's not like we're talking a lot of rotation to get into a tooth groove. I'd suggest finding a qualified armorer in your area to help you finish installation. There's no reason to use shims on a barrel installation. If you have to, something's out of spec and I'd rather send it back to BCM for replacement.
    Semper Paratus Certified AR15 Armorer

  8. #8
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    Try another nut, first. Otherwise, Brownells makes a receiver face mandrel that you use with lapping compound and chuck in a drill. Usually just barely enough to break the ano will do it. Don't go too far.
    Duane Liptak, Jr.
    Executive Vice President
    Magpul Industries

    info@magpulcore.com

    This is a personal account linked to a personal e-mail. Company affiliation and titles are provided purely for transparency requirements of the host site. Although factual company information may be shared through this account, any opinions expressed are solely those of the account holder, and not necessarily those of Magpul Industries or subsidiaries.

  9. #9
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    First I would say make sure your torque is ft pounds and not inch pounds haha it happens.

    Check the mating surface of the receiver and the barrel extension make sure they are clean, I like a light film of oil but only personal preference.

    Torque, break torque and re torque to 40 ft pounds if not aligned move up to no more than 80 ft pounds

    If still no dice. Check with the rail manufacturer for any possible defects of the barrel nut.

    Since BCM has a good track record for making outstanding products I wouldn't be lapping or modifying anything.

    If any of my remarks are not comfortable for you do your homework on a gunsmith that does good work with ARs and have them do the work
    Last edited by koniz; 12-16-13 at 21:09. Reason: Forgot a few words
    Former LMT test/ assembly/ machinist
    Former Rock Island Arsenal / machinist

  10. #10
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    I keep a few barrel nuts around just because of this issue. QA has slipped over the years and sometimes I buy what I think is first quality from Brownells or Midway and it may take several barrel nuts to get one to line up correctly. Same with the threading on upper receivers. Sometimes they are just off enough to scare you using the wrench.

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