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Old September 23, 2020, 08:51 PM   #1
napg19
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BAR barrel nut torque on AR15

I have bar barrel nut torqued to 42ft lbs. Gas tube goes in upper reciever but is slightly off to one side. If I lossen bar nut so slightly to align gas tube to be straight will this affect the entire torque of nut. In other words should I retorqe the entire nut again. Thanks.
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Old September 24, 2020, 01:39 AM   #2
Scorch
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42 ft-lbs is a lot for an AR barrel nut. I torque the barrel nut to 28-36 ft-lbs when I assemble them. If I have to torque more to get the gas tube to align, I use shims.
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Old September 24, 2020, 10:42 AM   #3
Sharkbite
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Mil spec torque value is 30-80ft/lbs. thats a HUGE range. That range is to allow you to line up the gas tube.

So.. get the tubed lines up inside that range and you are good
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Old September 24, 2020, 01:52 PM   #4
FrankenMauser
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BAR barrel nuts come with shims. Use your shims.
If the rifle came with that barrel nut, order some shims.

Quote:
Mil spec torque value is 30-80ft/lbs.
That's with the specified Mil adapter, in the specified orientation. Different tool, different orientation, totally different game.
Torque values are not useful for comparison here.
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Old September 24, 2020, 06:41 PM   #5
44 AMP
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TM 9-1005-249-34 (that we used in the 70s for the M16/A1) said torque to 35-40 ft/lbs, then tighten to align the nut for the gas tube.

It worked then but back then in the Army we were all using the same stuff. TOday with who knows how many companies making AR parts, who can say??
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Old September 26, 2020, 12:12 AM   #6
ed308
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Quote:
If I lossen bar nut so slightly to align gas tube to be straight will this affect the entire torque of nut. In other words should I retorqe the entire nut again.


I've backed off on the barrel before and didn't experience any problems. Make sure to torque the nut at 90 degs with the wrench and use grease on the threads. That's needed to get an accurate reading of the torque. If you stay in the 30-45 lb. range you should be fine. Shims help with indexing the gas tube, especially if a Aero BAR nut. I done a bunch of builds with Aero's hand guards and their BAR nuts. Dislike the design. They can be a pain IMO.
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Old September 29, 2020, 03:37 PM   #7
napg19
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Thanks for the info. Backed off the nut slightly and replaced gas tube. Perfect gas tube to bcg fit. Thanks.
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Old September 30, 2020, 06:12 PM   #8
Dfariswheel
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Many of the top builders use the "Three times tight" method.

First they coat the nut threads with a NON-graphite anti-seize compound.
NEVER use graphite around an aluminum part, graphite damages aluminum.

With the threads coated, tighten the nut to just over the minimum to mid range torque, then back it off and tighten again, back it off and tighten the last time.
This tighten-loosen process force mates the screw threads.

Once you've tightened it the last time, check where the notches for the gas tube are.
Most builders just muscle the nut to align with the gas tube instead of backing it off.
If it's too far, they continue loosening and tightening the nut.
Each time the nut will screw on a little farther until the groove does align.

Backing the nut off any real amount to align risks vibration of the barrel ruining accuracy.

There are any number of ways to fit a barrel but this is one many top builders use.
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