TDP says to inline with the wrench…but seen places and recommend to do it 90 degrees.
The torque wrench and barrel nut tool should be perpendicular to each other. Torque works on force and distance, lengthening the moment arm by having the torque wrench and barrel nut tool parallel to each other will give you a higher torque than the wrench was calibrated for.
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In line. One shouldn’t be going much above 40 lb feet anyway.
It won’t give a higher torque than it was rated for, but will measure lower than actual torque on the nut itself. If you want to get actual nut torque value, you need to add the distance from the nut to the attachment point on the wrench and then calculate the torque value read on your wrench which should be expected. I would assume that if using an armorers wrench, and using gorilla math, that torquing to about 36-38 foot pounds would be about 40-50 foot pounds at the nut.
90 degrees gives a “true” torque reading because it factors out the additional torque added by the mechanical advantage of the 1/2" square drive hole being a certain distance from the center line of the barrel nut in this case.
That sounds great except for the fact that the torque specs everyone uses have already factored in the added distance of the military barrel wrench when it is used inline as the manual states should be done. (please consult the latest manuals).
That being said the range of the acceptable torque is so large the difference is of no concern unless perhaps you are using 90 degrees at the max value.
I have had enough experience that I rarely need to use a torque wrench these days but a beginner should until they have a few builds under their belt.
I should have been more clear, but this is what I was trying to say. The actual torque will be higher than what the wrench is indicating. Thanks for cleaning up my response!
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If the OP or anyone else is interested in doing the math, the proper barrel extension tool (when used properly in the extended “in-line” position) will give you 2.0" of extension (measured from the center of the barrel nut to the center of the attachment point for the torque wrench.
Joe Mamma
It doesn’t really matter… as far as GI nuts go. There’s really only one correct position for any given GI nut. You don’t even really need a torque wrench if you’re even slightly mechanically inclined.
Agreed. Once you master those damn things, almost every other barrel nut will seem like childs play.
I agree with Mark & IG. Once you understand the principle behind tightening the barrel nut, a torque wrench isn’t needed.
As far as the correct procedure is concerned, follow the manual. It specifies which wrench is to be used with which wrench and what method is used. If the manual states 40 ft/lbs with the tool inline with the wrench, that’s what you must do. Turning the tool 90 degrees or calculating the arm to compensate for the added length is simply wrong
Unless using a USGI barrel nut. 
Per the manual, it is inline with the torque wrench with a torque value of 30-80 ft./lbs.
Per the manual, it is inline with the torque wrench with a torque value of 30-80 ft./lbs.
I don’t use a torque wrench anymore. I use to. If I assembling an upper for someone I usually break out the torque wrench, just to show them what it is supposed to be.
No.
It will give a distance closer to “true” but it will still be off a bit…
A is the length of the torque wrench for the correct torque.
B is the distance from the center of the socket lug to the center of the wrenching ‘flats’
C is the actual torquing distance.
The actual torque applied with the wrench adapter at 90 degrees will be in proportion to: C = [(A^2) + (B^2)]^0.5
Very close to A but not quite.
That’s not true. Only the distance perpendicular to the force matters. A is the moment arm.
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Here are some helpful resources to get you up to speed:
http://www.cncexpo.com/TorqueAdapter.aspx
https://www.motorcraftservice.com/renderers/torquewrench/wrench_formula_main_en.asp
https://www.dmctools.com/Products/torque_conversion_charts.html
http://www.trialsnuts.com/TORQUED.pdf
http://www.engineersedge.com/manufacturing_spec/torque_wrench_1.htm
I had always done perpendicular because of physics, but if that’s already taken into account I’ll go in line. I’ve gotten spoiled by my Aero Precision uppers lately, and not having to line up a barrel nut… but I wish the handguard wasn’t so big.
I agree with mark. If you’re using a standard GI Barrel nut, Just crank it down til its alligned
Isn’t this what most here give so $hit to DPMS, Bushmaster, Olympic and every other brand that is not tier 1 for doing. Calling it a lack of quality control.