Loctite's longevity on an AR15's barrel nut?

[Religious Shooter]

I had my barrel changed and my local smith said that the barrel/handguard nut came off easy. He was prepared for a struggle and he was surprised that it came off so easily.

The upper/barrel was more than three years old and had about 15K+ rounds through it. The upper was initially put together by a well known gunsmith. I'm fairly confident that he would have used loctite on the barrel nut. But maybe he didn't?

So I'm thinking... maybe the problem with the upper was the lack of effective loctite on the barrel nut and that the barrel wasn't that worn out.

When you changed out your barrel and you KNOW red loctite was used... has it always been a big a** pain to take it out? Or in some cases did you find it easy to take out and that the loctite had degraded due to heat and age?

This upper/barrel would hold about 1.5 MOA. But as it got hot it would do 3-4 MOA with a vertical dispersion. Does this sound like a problem caused by not having (effective) loctite on the barrel nut?

I'm trying to figure out if it would be a good idea (next time) to reassemble an upper to see if the accuracy/consistency comes back instead of automatically assuming that the barrel was worn out.

[Bryan 45]

I have never heard of anyone that knows the proper way to assemble an AR using loctite of any kind on the barrel nut. About all the instructions I've ever seen recommend 30-80 ft lbs of torque applied to the barrel nut. I've taken apart several factory rifles from RRA, DPMS, and even a couple old Colt A1 uppers and never seen any signs of loctite.

As long as the barrel wasn't wiggle it with your hand loose in the receiver, I doubt the tightness of the nut had anything to do with your drop in accuracy. The gas tube keeps the barrel nut from turning more than a degree or two, so even a hand tight barrel nut isn't going to cause the barrel to fall out of the receiver.

15K rounds quite a bit on a barrel. It was probably just getting worn out.

[uno5885]

Agreed on the loctite. I have been an AR armorer for years and have build or worked on many AR's and have never used loctite on the barrel. Like Bryan said the toque spec is 30-80 lbs so if it was on the lower end of that of course it is easier to take apart but I would never but loctite on a barrel.

[caspian guy]

That isn't someplace I'd want loctite...

In fact I usually use anti-sieze compound on the threads between the upper and the barrel nut to prevent galling. Otherwise getting the barrel nut off come time to rebarrel can be a real chore...

At 15k rounds likely the barrel is worn out.

[Big Bore]

You use the loctite where the barrel goes into receiver, not on the threads. It keeps the barrel from "walking" when it heats up. I use the blue Loctite. I have not had to tear one apart yet but a little heat should loosen it right up.

Before I started doing this I have had 2 rifles barrrels work loose. One is a stock Bushmaster Varminter that is only used for hunting and does not have many rounds through it and one of my 3 gun rifles worked loose and I couldn't figure out why I was missing such easy targets. I Loctited both and have had no issues since.

What kind of barrel is it? Some barrels can get 15k plus.

With the groups opening up when it gets hot I would say it was a little loose in the receiver. But since you already have it torn out you might as well replace it.

Edited August 22, 2010 by Big Bore

[boomfab]

You don't want loctite on the barrel nut threads.

You want moly grease with no graphite added.

[00bullitt]

Vertical stringing is usually a sign of barrel movement as opposed to a scattered group from a worn out throat. But thats not to say the barrel is not shot out with 15k rounds through it. A good barrel can go 15-20k. But the norm is more like 10k when you see accuracy start to degrade.

Sounds like the barrel may have not have been tightened to spec originally and over the years of shooting with expansion and contraction it was moving around in the receiver. I use an anti seize compound and tighten to at least 40 ft. lbs. when I assemble uppers. the only time I have used red loctite is on the Clark carbon fiber handguard with the aluminum barrel nut that has to be tightened with a strap wrench.

[twodownzero]

You use the loctite where the barrel goes into receiver, not on the threads. It keeps the barrel from "walking" when it heats up. I use the blue Loctite. I have not had to tear one apart yet but a little heat should loosen it right up.

Before I started doing this I have had 2 rifles barrrels work loose. One is a stock Bushmaster Varminter that is only used for hunting and does not have many rounds through it and one of my 3 gun rifles worked loose and I couldn't figure out why I was missing such easy targets. I Loctited both and have had no issues since.

What kind of barrel is it? Some barrels can get 15k plus.

With the groups opening up when it gets hot I would say it was a little loose in the receiver. But since you already have it torn out you might as well replace it.

That type of loctite isn't made for that application. There is a green, "sleeve" loctite made for what you're talking about (to tighten interference fits).

Regular loctite is designed as a threadlocker only.

+1 on the others' statements about not using loctite on a barrel thread. I'm willing to bet it'd get hot enough to break down anyway.

Edited August 22, 2010 by twodownzero

[GentlemanJim]

Anti sieze on the barrel nut(or light oil)

Torque to 60 fp is optimum...grind off a tooth or slot a hole in the barrel nut to get there

An upper reciever that has a loose fit on the barrel will string shots

High temp RTV like copper silicone will work well to stabilize the barrel, as will several locktite products

You can make a sloppy upper run well this way, but a tight fit between barrel and reciever is best

Its good to ckeck the upper for square where the barrel ring meets it...if its off square, the barrel will not be seated true

This will also string shots

JMHO...Jim