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AR Barrel Nut Alignment

Discussion in 'Rifle Country' started by Shimitup, Jan 25, 2020.

  1. Shimitup

    Shimitup Member

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    I just finished my first AR last week. Just wanted to know if anyone has issues with barrel nut torque specs not quite hitting 30 ft lbs on the first notch and hitting 80 well before the next one lines up? Did I get unlucky or is this sort of routine? I used white lithium grease on the threads and a super grade of EP high moly content between the nut and barrel flange so as to eliminate rotational force against the index pin and the upper.

    I ended up solving my problem with a lathe but most folks don't have a lathe. i shaved off .0028 which is more than I wanted but it took that to clean up the face of the upper which was out just that much. Upon trying to retorque I ended up with the same problem.... Duh that's the thread pitch per 1/20th of a turn, back to the lathe for another .0015. I ended up lining up for the gas tube at 70 ft lbs so I'm pretty happy, although a little disappointed that things were a little out of square.
     
  2. IndianaBoy

    IndianaBoy Member

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    Grind off a tooth if you need to. You don't need all of them for the barrel nut wrench, and they don't do anything else structurally.
     
  3. IndianaBoy

    IndianaBoy Member

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    None of my hand guards or barrel nuts that I use now require indexing the barrel nut.


    Old guns, that was the way.

    New guns, there is no reason to do it that way.
     
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  4. someguy2800

    someguy2800 Member

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    They make shims that go between the barrel shoulder and the nut if you need too. With some free float handguard nuts this is pretty much a requirement to get them aligned straight.
     
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  5. Shimitup

    Shimitup Member

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    Yeah, I gave that some thought until I remembered the indexing nubs inside the Magpul handguard that I've already planned on using.
     
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  6. BSA1

    BSA1 member

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    Ditto on shims.

    I learned about needing shims on my latest build. I brought a couple of shim packages from Brownells and it is a simple matter of mixing the different sizes for the perfect barrel nut fit.
     
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  7. Skylerbone

    Skylerbone Member

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    Easier than the lathe and economical enough for anyone who assembles their own. Still envious of your lathe, but for the issue of alignment a lapping kit solves it.



    A489B0A5-E387-46CE-98E1-95F558D1FDDF.jpeg
     
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  8. Demi-human

    Demi-human Member

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    You are familiar with the Aero Enhanced Uppers, correct?
    Would this kit work with those as well?


    I seem to be having issues...:(
     
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  9. Skylerbone

    Skylerbone Member

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    It should, assuming the barrel nut has not bottomed out against the upper with the barrel installed. You do not want to grind away forever at the forward edge with a lapping kit, I used it for timing to torque as suggested in a post by @Varminterror I believe it was. The topic at hand was necessary tools for correct assembly of an AR vs. winging everything and hoping it works.

    This worked for the one time I’ve used it (so far) and I plan on assembling future uppers which makes the investment ever more useful.
     
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  10. mshootnit

    mshootnit Member

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    It is routine. If I get one to line up right, I start to peer out of my blinds to see if anyone is watching.
     
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  11. BigBore45

    BigBore45 Member

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    Back of and re tighten. 3 or 4 times will change seating and thread mating. Should get you there.
     
  12. shoobe01

    shoobe01 Member

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    This.

    Learned long ago from other machine shop work so did it automatically once I started getting to wrenching uppers. Not sure if some of the nut stretch is permanent, or it's just getting the mating surfaces flat, but I've had to do this on all of them. Absolutely will not line up between 30 and 80 the first time, so I just do it a few times until it does align before 80.
     
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  13. Skylerbone

    Skylerbone Member

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    It may be presumptuous on my part that a guy who owns a metal lathe and (by context) a torque wrench knows how to correctly torque a nut, be it barrel or otherwise. I’m sticking with my gut on this one and believing he knows the drill but it would not align without correction.
     
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  14. Shimitup

    Shimitup Member

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    I did do that, didn't work for me. It did change just a little during the first couple of seatings then stabilized still well short of the mark. I use the old beam type Craftsman wrench, I like to approach torque slow and steady and watch the progression on the scale. An old habit from engine building days to be sure of uniform bolt stretch. BTW it's beautiful outside and a good day to go run the thing! Range report will happen. Sight in and chrono happen for all the ammo I've been making for it.
     
    Last edited: Jan 26, 2020
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  15. Varminterror

    Varminterror Member

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    Other’s might have suggested it too, but I know I certainly have and do suggest it here. Super inexpensive and doubly beneficial - eliminate some inconsistency, and control torque AND alignment of the barrel nut to the gas tube simultaneously.
     
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  16. Shimitup

    Shimitup Member

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    Brief range report. Fun, fun, fun. It's a sweet shooter, got the red dot dialed in in about 4 shots patching the bore between shots, It's amazing how much smoother the bore feels after just a few shots. I had lots of chronographing to do so I got right down to business with six different loads six of each. It consumed them all just fine even some mild ones at around 2600 fps, all brass seemed to dump at 7ft 3:30. I need to get used to using the red dot and the gun before I settle down and try for accuracy.

    IMG_20200126_162720839_HDR.jpg
     
  17. ApacheCoTodd

    ApacheCoTodd Member

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    Lathes?.... Shims?.....

    I have built literally hundreds of uppers and many hundreds at that and never once considered either.

    Have never had an issue either.

    Most I've ever done is to tighten till I can't reach the next tooth or hole then, back it out, clean threads and readdress the nut.

    If you can't make it to the one you think you want, leave it at the last one passed.

    This really doesn't need to be over-thought.

    Those index points are 18 degrees apart on center with a couple degrees play either side of center.

    So each *tooth* moves the nut forward, what.... .027777 of an inch?

    Todd.
     
    Last edited: Jan 27, 2020
  18. Shimitup

    Shimitup Member

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    I'm probably just picky but I just didn't want to leave the nut just shy of 30 ft.lbs, especially being my first build and I just don't know what I can get away with. The thread pitch is 18 so 1/18th= .055 / 20 is .0027 so if you hit 80 ft. lb. and you're right smack in the middle of a tooth you can remove .00135 and you end up torquing to 80 right in the middle of the notch 1/40 of a turn more (9 deg).
     
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