AR Barrel Nut Question--LocTite?

[sschudalla]

I have a question about barrel nut tightness. I recently had a gunsmith remove my standard free float rail from my DPMS LR308 and I added a Troy Industries TRX Battlerail. I took the rifle out to the range on last Friday and I had an issue that I wanted to ask the experts. Right as I was about ready to head home from the range I noticed the rail was loose. Upon taking it off to investigate at the range I revealed the Barrel nut that runs over the barrel and attaches the barrel to the upper receiver. The rail attaches to the barrel nut with two clamping allen screws. I also did notice that my accuracy was worse than norm but chalked it up to my meager shooting that day--thought no big deal at the time. Usually my rifle can shoot 1MOA and I was far from that. My concern is that I noticed the barrel nut had become semi-loose as well!! I did not have my armorers wrench with me so that ended the day at the range form me (no problem--was there for 6 hours!). I brought it home and unscrewed the barrel nut to see how loose it was and found it was only finger tight. The directions that came from troy state it should be tightened down to 30-50 ft lbs of torque. I am wondering what you think I should do.. Should I be angry at the gunsmith and have him address it for free? Is this normal and have you ever had this happen? Should I just tighten it up myself and call it a day? Is there a threadlock that can be used to keep it down under the firing of my rifle as it seems like it vibrated loose? It seems like a pretty dangerous condition so I want to get a lot of advice before proceeding.

As always, any help or thoughts are appreciated

 

[WardenWolf]

My personal opinion is that it just vibrated loose. Fix it yourself. You've got 2 good options: blue Loctite (formula 243) or teflon. I recommend blue Loctite. The stuff is easily breakable with standard wrenches or other tools, and will hold up to abuse. It's also easy to get out, unlike teflon.

 

[taliv]

read the mfg instructions as it varies.


however, usually, you put grease on the barrel nut to keep it from galling and torque it properly, instead of using loc tite

 

[TonyAngel]

Don't use loctite on the barrel nut. Really, it won't work anyway. Loctite doesn't do well with heat and the barrel nut area is where things get the hottest.

I've seen what happened to you on quite a few occassions. I'm just guessing, but my guess is that when your smith installed your rail, the notch for the gas tube didn't align with the opening in the receiver when it was torqued to spec. Odds are that he would had to have over tightened the nut to get it to the next notch and backing off to the next lower notch left the nut under torqued, which caused it to come loose.

When I run into this problem I usually do one of two things. The first, if possible, is to just try a different barrel nut. If that isn't possible or just doesn't do it, I lap 1/1000th off of the face of the receiver so that I can get to the next notch on the nut. Like I said though, I'm just guessing.

My suggestion would be to put a torque wrench on it and torque it to the proper spec and see where that leaves you. I've never seen a properly torqued nut come loose, but of course, I haven't seen everything.

 

[TonyAngel]

Oh, and Taliv is right about the grease. Don't forget to do that.

 

[W.E.G.]

The barrel nut must be installed to correct torque spec.

Once this is done, there is no need for Loctite.

You wouldn't put Loctite on the lug-nuts on your car.
...and you wouldn't want to drive a car where the only force securing the lug-nuts was some sort of glue.

There is no room for monkey-business on barrel nuts.
Figure out how to do it right yourself, or hire somebody who knows what they are doing to do it for you.

 

[sschudalla]

Lot of good information and I appreciate all of it. I looked up torques and they are going for 150+ so I think I am going to take it to a smith (different one) to lap and torque properly rather than me just guessing in the basement with my AR wrench. I noticed there is a good deal of oil around the ring but no grease. There is a gunsmith at my local range that seems solid (Accuracy Speaks is the name if you know anything Warden let me know). This way I can get that trigger I have wanted for a while anyway!! Thanks for the help guys. Once again, glad I asked and didnt just go along blindly. Others experience is real helpful!!

 

[Tirod]

There is only a range of barrel nut torque, NOT a specific number to shoot for. It's an indicated measure, not actual, because the tool specified when coupled to a torque wrench actually delivers more leverage.

The procedure is designed to set the threads and eliminate burrs by tightening three times to at least 30 foot pounds, then turning the barrel nut to line up, not to exceed 80 foot pounds. That's using greased threads, not dry, which actually delivers more pressure on the threads than the indicated number. The result is a procedure mostly designed to keep a semi skilled 20 year old armorer from damaging things, using tools really needed for a half dozen other organic weapons - mostly machine guns.

Mounting barrel nuts can be done with a pair of channel lock pliers, the skill of the user goes a lot further than a collection of tools. Find an AR knowledgeable smith, possibly the one contracted to service the local PD's and Sheriff. There are a lot of smiths who never worked on AR's before getting walk in trade now, and it's not always their area of expertise. They won't say no to a cash customer.

 

[bbuddtec]

First off, that gunsmith screwed up. The gas tube keeps the possibility of the barrell nut loosening more than 1/100th of a turn, I don't know the exact amount, but if you look at it, you get my drift.

zzzz....

 

[madcratebuilder]

So far the specs everyone has given you are for the AR15. You have a AR10 platform rifle, larger barrel nut and higher torque specs.

From the AR10 owner manual on barrel install.

1. Grease the threads in the upper receiver lightly with a heavy duty grease. Install the barrel nut and lock ring to the upper receiver. Torque the barrel nut onto the upper receiver to 50 ft.lb. Then loosen the barrel nut and retorque to 60 ft.lb. Then loosen and retorque to 70 ft.lb. Then tighten further as needed to align the gas tube hole in the upper receiver to match the next hole of the barrel nut to allow the gas tube to pass freely through the nut and rest freely in the center of the upper receiver.

The above is for the ArmaLite AR10, I would contact DPMS and confirm if they recommend the same torque specs.

Do not use the AR15 specs of 30-30-30-50ftlbs.

 

[Zerodefect]

Just be sure your talking about the actual barrel nut.

Not a ring attached to the nut that holds the rails onto the nut. Seen someone make that mistake before.

 

[kwelz]

I'm just going to paraphrase from Derrik Martin, from Accuracy Speaks... "I pull the nut up snug where I feel it not moving, then check for alignment with the keyhole and advance it to allow the gas tube correctly. That comes to just over 5-10 lbs. I don't use anti-seize, just blue loctite."

Wow really? I would never let a bubba like that touch one of my guns.

 

[gotigers]

The barrel nut threads should have a molly lube applied to prevent seizing. Loctite wont work. The heat will degrade it.

The rail nut and rail set screws should have a little loctite without any problem.

 

[gotigers]

I'm just going to paraphrase from Derrik Martin, from Accuracy Speaks... "I pull the nut up snug where I feel it not moving, then check for alignment with the keyhole and advance it to allow the gas tube correctly. That comes to just over 5-10 lbs. I don't use anti-seize, just blue loctite."

bad advice

 

[mrmeval]

Blue loctite won't hold with heat. There's a chart that shows temperature derating. You won't find this on the consumer technical data sheet. :/

https://tds.us.henkel.com//NA/UT/HNAUTTDS.nsf/web/4F5DE4CF912A71D7882571870000D60D/$File/242-EN.pdf

Based on a brief look none of the commonly available threadlockers are suitable for that application.

 

[mljdeckard]

I haven't bought one lately, but I didn't think that torque wrenches were that expensive. Talk to places that rent tools, like your local auto-parts store, to see if they rent one. what I have found is, a torque-wrench is one of those tools that you find all kinds of things it's useful for once you have it, that you talked yourself into living without for a long time.

 

[bbuddtec]

Know what holds with heat??? A stainless steel tube down the keyway. So how did the barrell get loose?

Personally, I think anti-seize is the way to go but if you want to re-build your AR10, advise from anywhere should be 1/10th of the research you do.

 

[WNTFW]

I use the never seize also.

 

[Zonie]

The Army technical manual say to use moly grease on the threads. It also says to torque to specs three times, as in -tight-loosen-tight-loosen-tight. On the third one, tighten to minimum torque specs and then only tighten more if you need to get the gas tube to line up. Also be sure to not tighten beyond the maximum torque specs.

This is for M16s, but I'm sure it applies to AR-10 types as well; although there are probably different torque specs for the AR-10.

 

[Kwanger]

People get confused about the whole loctite thing with AR15s. The use of loctite as advocated by several accuracy gurus is on the barrel extension and inside the receiver where the receiver and barrel mate together - not on the nut threads, which should be moly-greased and torqued to the respective 30-80ft/lbs.

The purpose for the blue loctite on the barrel extension is to act as bedding, particularly in a barrel/receiver combo where the tolerances are loose. Once the loctite cures, it acts to ensure the barrel extension is firmly held by the entire receiver, rather than just relying on the front face and barrel nut torque.

Regarding loctite in that spot breaking down under heat - not a problem. The majority of the heat is generated forward of the barrel extension. In the use I have described, even if the loctite does break down a little over time due to repeated heating/cooling, it still continues to do its job effectively mating the barrel to the receiver.

People often have the wrong idea about loctite, they have visions of it melting, etc. It does not melt - heat simply reduces its shear strength so you can get it undone; you always have to scrape the dry residue off, it won't get runny and melt away.