AR barrel nut torque specs

[cactusbrew]

Lets talk AR barrel nut torque specs.

I have seen in a few threads the random comment about "more torque, more consistency," and wanted to start a separate thread on this. Everywhere you read, it says to torque a barrel from 30 to 80 ft lbs. Some specific manufacturers actually give you a number of 35 lbs or 45 lbs, etc.

I saw a comment on another thread stating to torque to 75 lbs for most cold/hot consistency. So what does everyone else think on this topic? Whats the consensus?

Is the standard for a rifle now 75 lbs or whats everyone doing?

[IntenseImage]

Kinda depends on the barrel nut. For my wife's ALG handguard we just had to line a specific mark on the tool up with TDC of the upper. For the one I just did with my F1 M7M, I tried to hit 70 ft/lbs and the tool spread and rounded the nut before I could hit that number.

[outerlimits]

Last 4 builds using JP barrel/nut has got me to about 60. Never beyond. Remember to tighten, then loosen, then torque.

[P.E. Kelley]

Last 4 builds using JP barrel/nut has got me to about 60. Never beyond. Remember to tighten, then loosen, then torque.

Yea..that's the right way...but then again...I like the "ol' run her up till she strips and back of a flat!" (or was that my first wife?)

[Stlhead]

Seekins mono uppers and Ti nuts need every bit of 75# and the threads need to be bone dry with at least 3 cycles. Or else.....

[MickB]

Grease the threads of the upper, then tighten up snug and loosen 3 times. By doing this you are seating the threads of the barrel nut to the upper.

At this point, when you snug up again, you should have the tooth of your barrel nut at ~12 o'clock (or half way to clearing the gas tube hole) and ~30-40lbs.

Tightening from this point will get you to 70-85lbs.

While on this subject, I have a related question. How tight should the barrel extension fit in the upper receiver?

Is a tight fit better for accuracy?

How tight is good enough (should the barrel not drop out of the receiver when pointing down with no barrel nut in place)?
Should I use Loctite or shim stock for a loose barrel?

Does this even matter when the barrel nut is torqued to 70-80 lbs?

Mick

Edited January 4, 2016 by MickB

[openclassterror]

With our hand guard design, we found that the least amount of torque that will stay tight through hot/cold cycles gives best accuracy, AS LONG AS THE BARREL EXTENSION FITS THE RECEIVER SNUGLY. If the extension fits like a hotdog in a hallway, either shim/ Loctite, or else you have to torque to 75+ to keep the barrel from squirming. If the extension fits, we torque to 35-40ft/lbs, using the tight, loose, tight, loose, torque it method. I use silver anti-seize on the threads. BUT, this is purely what testing showed on OUR handguard design. May not hold true for all, or even any, others. Remember that it is a V-thread, so once you exceed the modulus of elasticity for the wall thickness between the nut and the barrel, it actually starts collapsing and tightens the gap around the barrel extension. That is why a sloppy extension fit doesn't matter if you are going to torque it to the maximum. If you don't believe me, put a 1" stub where the extension goes, and use the nut to clamp a backwards extension in place (so you have the shoulder to torque against). It WILL clamp down on the 1" diameter once you have enough torque.

[e5young]

My buddy did 35 on my AR because that was all it took to line it up, but ive been told that 40 is more optimal...i could be wrong though...

[cactusbrew]

openclassterror

Do you feel a need to Loctite the extension on all installations or only if its a loose fit? Have you done tests to see if loctiting a tight extension effects accuracy or matters at all?

Thanks

[MarkCO]

If you are using good parts, 35 or 75 won't affect cold bore accuracy. However, when you get the set-up hot, the lower torque levels have more thermal drift.

I have found the best accuracy in the 75 to 100 ft-lbs range, however, I only use 7075T6 uppers that are almost 50% stronger than standard 6061 uppers. If you have a loose extension fit, more torque will help and at lower torque the thermal drift will be more pronounced.

I have found what Tom posted in #7 to be true for almost all set-ups. I also use the silver anti-seize and do the three times torque, release and torque process.

[openclassterror]

openclassterror

Do you feel a need to Loctite the extension on all installations or only if its a loose fit? Have you done tests to see if loctiting a tight extension effects accuracy or matters at all?

Thanks

I haven't tested the effects of Loctite on snug fitting extensions, because I don't want to fight it when the barrel has to come off. I use Loctite only as a bandaid fix on sloppy receivers. For several years now, I have just selected the best receivers for custom builds with our components and save the sloppy ones for Mil-spec type builds where I can torque the crap out of the castle nut. This plan doesn't work for the home-enthusiast, who can't pick through 20-50 uppers at a time for the good ones.

[MarkCO]

Realize that Loctite creates a chemical oxidation reaction (corrosion) and only works on activated metals. Hardcoat anodized aluminum is a passivated metal. Loctite is the wrong material to use on an upper to tighten the fit.

[Stlhead]

I am not a locktite salesman, but I have used it to great effect on anodized aluminum parts. Are you certain of how it works? From what I have read the reaction is not a surface corrosion, but a chemical bond that is catalyzed by certain metals, and the primer can make provide the needed reaction if there is no iron present. Or the manufacturer could be a dirty fibber, who knows?

[nheiny13]

Realize that Loctite creates a chemical oxidation reaction (corrosion) and only works on activated metals. Hardcoat anodized aluminum is a passivated metal. Loctite is the wrong material to use on an upper to tighten the fit.

How do you tighten the fit?

[kurtm]

I've shimmed and I've use Loc-Tite. Both gave the desired result of NO DRIFT, or wondering accuracy. I usually use Blue Loc-Tite, no need for red. and Green wicking also fills the gap, but WILL get into the threads of the upper. I like the shim method the best. I have never really reefed on a barrel nut, but then again I don't run them very loose either. Tom is absolutely right! If you torque the snot out of it, it will collapse down and hold, but I like to support the entire extension in the upper.

[openclassterror]

On the guns I have loctited and then later dis-assembled, the Loctite activated thru contact with the barrel extension, but didn't bond to the upper. Keep in mind, though, that there are machining marks in the bore of the receiver, so the Loctite forms a MECHANICAL bond by filling the surface imperfections even if it doesn't glue the two together. So, after you knock the barrel out of the receiver with a hammer and a long rod to act as a makeshift punch, the Loctite stays stuck to the extension but not the receiver. My experience with Loctite and AR uppers is confined to Red (271).

[MickB]

What are you guys using for shim material? 0.001" stainless?

Loctite I have plenty of.

Mick

[MarkCO]

I have a few pieces of shim steel I got several years ago, stainless and tempered blue spring steel. You can buy an assortment at Grainger at a premium price. I went to MSC and picked through a scrap pile for mine. They charged me $1.

[kurtm]

Brownells sells all sorts of shim stock, and fairly reasonable.

[mpeltier]

Lets talk AR barrel nut torque specs.

I have seen in a few threads the random comment about "more torque, more consistency," and wanted to start a separate thread on this. Everywhere you read, it says to torque a barrel from 30 to 80 ft lbs. Some specific manufacturers actually give you a number of 35 lbs or 45 lbs, etc.

I saw a comment on another thread stating to torque to 75 lbs for most cold/hot consistency. So what does everyone else think on this topic? Whats the consensus?

Is the standard for a rifle now 75 lbs or whats everyone doing?

Colts Armorers manual is a solid referance. It uses a starting torque value of 30 ft/lbs for the tighten/loosen sequence and gives a max torque value of 80 ft/lbs. Bear in mind this is with a 7075 T6 upper and a mil spec bbl nut. If your using an alloy of lesser quality or an aluminum bbl nut I would recommend a lower max value.

I typically start at the lower torque value for initial sequence tightening and for final tightening, adjust my torque wrench to 50lb for steel bbl nuts or 40 lbs for aluminum and when the wrench clicks, keep tightening only to the next gas tube hole if necessary. Never had any issues with wandering groups using this method.

Edited January 8, 2016 by mpeltier