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

  1. #11
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    Quote Originally Posted by ASH556 View Post
    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.
    I've assembled a few hundred uppers at my last employer and it does happen. Annoying as hell when it does. Not as bad when it's just a plain GI barrel nut where I could just go to the spare parts and try a few until one works. With some of the rail systems that used their own nuts it was a bitch.
    It doesn't mean anything is out of spec, just that both the upper and the nut could both be at the large end of the spec. The plus and minus that every spec has (that's what a tolerance is by the way, the plus or minus of the dimension of a part, not how tight or loose the parts fit together... that's a side effect of extremely loose tolerances)

  2. #12
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    How much do you need to exceed the max torque to get it to work?
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  3. #13
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    This same topic is running strong on another site, dedicated to 3g competition, brianenos.com, in the technical rifle section. While a lot of feedback is similar to what is posted here, namely one should be able to obtain gas tube clearance while remaining in the recommended torque range of 35-80 ft-lbs, a respected poster stated that he has had no loss of accuracy with higher torque, within reason. This was also confirmed by a respected poster here, Robb Jensen in a PM.
    After conversing with these helpful folks, I left my rebuild alone, having obtained alignment at 85 ft-lbs. A take away from the discussion at be.com is that removing anodizing via lapping is a bad idea as it opens the possibility of galvanic corrosion between the barrel extension and receiver face.

    Mark

  4. #14
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    Well, I loosened and retorqued to 80ft-lbs 20 times. It got a little better, but it seemed like it stopped making progress. I added a small witness mark and saw that it stopped advancing after 9 or so "re-torques".

    I ended up torquing it to 84ft-lbs according to the electronic torque wrench from work, I'm sure it's about 90ft-lbs+ when you take the mechanical advantage of the adapter into effect. I torqued it and took off the nut to inspect the threads on the receiver and the nut, doesn't look like anything was damaged.

  5. #15
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    Mine torques right at 30, and lined up, right when it clicked. In fact, truth be told, its ever so slightly past where it needs to be, but the rail seems to be pretty level. I still know it bugs me, so I'll end up fixing it

    Sent from my RM-860_nam_usa_100 using Tapatalk

  6. #16
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    Quote Originally Posted by Jmanwit View Post
    Mine torques right at 30, and lined up, right when it clicked. In fact, truth be told, its ever so slightly past where it needs to be, but the rail seems to be pretty level. I still know it bugs me, so I'll end up fixing it

    Sent from my RM-860_nam_usa_100 using Tapatalk
    You mean above 30 in torque, or not properly aligned? lol, if not alligned straight why'd ya not just fix it and get it centered? Seems silly to leave something so easy to do off center.

    PS I think it was IG who mentioned he did the 3x method, but did not use grease until the 3rd and final torque. I could be wrong as I can't find the thread but prett sure I recall him saying thats how he did it.
    Last edited by discreet; 01-04-14 at 14:37.
    From TOS ... "buy the shit out of that thing, all the mil spec is just nonsense."

  7. #17
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    I did the 3x method, ima try a couple more than that again. In essence, with the wrench at 30, the min required, it is so minute, that unless you run your fingers down the side of the receiver, you wouldn't notice. I'm gonna redo it haha

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  8. #18
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    Quote Originally Posted by SPQR476 View Post
    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.
    It's a truing jig and i have one. Worked great.

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  9. #19
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    Quote Originally Posted by ASH556 View Post
    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.
    Guys, I'm gonna eat some crow on this statement. I've currently got a customer's upper (also with an MI barrel nut) and it just will not make it. 30 ft/lb is just past aligned and 80 is dead center of the next tooth. I've torqued and released more than a dozen times. I just got off the phone with MI and have another nut inbound. Hopefully it works...if not, we'll try a little lapping.
    Last edited by ASH556; 01-21-14 at 15:39.
    Semper Paratus Certified AR15 Armorer

  10. #20
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    You are a class act!
    Most folks would just move along and not admit they were wrong, if no one was watching over their shoulder.

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