Should a barrel nut on an AR ever be re-tightened?

[paul73]

I’m not sure about a quantified expected range, but later tonight I might be able to check my 20” service rifle target barrel and 20” SP1 pencil barrel with specific weights hanging off to see what kind of flex they show.

Ok. Ain’t there an other thing like drunken sledgehammering at precision machinery.

I took the mofo nut off. A 1000F heat gun and some hammer in the end as even maxed out 200lb/ft was not enough to break it free. I broke and cracked nylon upper cradle. Viced it on metal, hammer, and Then it moved.

My respect to LaRue. They mirror polished mating surfaces of upper and barrel.
Of not great news now. With nut off, there was almost 0 horizontal play, but there was a distinct amount of vertical play. I suspect I may be dropped rifle once, who knows.
Sucks.

Anyway, I got nut back at 80 lb/ft. Feel no excessive play now. If I feel like it I may get new upper and swap it out. Does not feel necessary now, but, will see.

 

[PappyM3]

My respect to LaRue. They mirror polished mating surfaces of upper and barrel.
Of not great news now. With nut off, there was almost 0 horizontal play, but there was a distinct amount of vertical play. I suspect I may be dropped rifle once, who knows.
Sucks.

Anyway, I got nut back at 80 lb/ft. Feel no excessive play now. If I feel like it I may get new upper and swap it out. Does not feel necessary now, but, will see.

Glad to hear it worked out.

When you say “mirror polished mating surfaces”, are you talking about the upper receiver being lapped?

 

[paul73]

Glad to hear it worked out.

When you say “mirror polished mating surfaces”, are you talking about the upper receiver being lapped?

View attachment 545810

I should have taken a picture.
Front is lapped - done like you have on shot, but the whole internal surface is also all polished on both upper insides and barrel outside part that slips into the upper. Had original lubricant on it also - still there after all the shots, and clean.

I had to take it off vise to re- insert the barrel it would not go in while upper was stressed. When free it went in with no gap nor play.

 

[1903Collector]

Is this is reference to the big thread of the barrel nut, or of the threaded connectors the JP handguard uses to attach to the barrel nut?

The barrel nut, not the tube threads.

I had an MSAR STG556 and I'm pretty sure the MD on that thing was red loc-tite'd on there. I. had the MD changed and Santurri had to use a torch to get the original one off.

 

[PatMcD]

Youve got to understand that no matter how tight that nut is, you still have 5 lbs of a 20" metal tube that is attached to an aluminum upper. There is going to be flex.

When in doubt, take it completely apart and put it back together.

If the barrel is a sloppy fit in the upper, I shim it with brass shim stock. Maybe it helps, maybe it doesn't; but once I do it, I don't worry about it until it's time to change the barrel.

 

[mac1911]

How could the barrel nut possible loosen? One of the notches has to be lined up with the gas tube that is installed after the barrel. The tube through this notch would prevent the barrel from loosening to any meaningful degree (probably just a fraction of a degree until blocked by the gas tube). The torque range is pretty wide - 30-80 ft lbs according to the Armalite instructor I took the class from.

I think a loose barrel nut even blocked by the gas tube could easily be felt , flopping no.
But if it was torqued correctly it not common to come loose.

 

[mac1911]

Red loctite is a solution for sell it and forget it model. To take anything apart that was on red is a huge pita. Especially a nut that was torqued to 80 ft/lb.

I bought a upper from a match shooter who basically gets a “new” barrel after 3500 rounds or so
He uses that gap filling lock tite stuff on his . Has no intention of spinning off the barrel. Sold it to me with receiver “permanently attached. Has mad a good range beater.

 

[paul73]

I bought a upper from a match shooter who basically gets a “new” barrel after 3500 rounds or so
He uses that gap filling lock tite stuff on his . Has no intention of spinning off the barrel. Sold it to me with receiver “permanently attached. Has mad a good range beater.

3500 rounds per barrel is not much. I hope mine will last longer, at at least 3/4 moa. But, it is what it is, of course.

 

[moojpg2]

+1 for the anti-seize. I realize too late for OP, but getting it torqued down with anti-seize I've never had one come loose including 6.5 Creedmoor and .458 socom.

the OP has probably never shot a rifle enough to have to replace a barrel. Red loctite is a c*** especially on a barrel nut.

That I can do.
Any idea how much flex in mm is allowed on a 20” heavy barrel? I can at least measure that.

The barrel is not flexing by pushing on it with your fingers, no way a 20" heavy barrel made out of stainless or 4150 steel is gonna flex significantly with your fingers, if you are pushing on the handguard to make the barrel flex it is the hand guard flexing, not the barrel. You could probably snap the upper reciever in half trying to flex that barrel any appreciable amount. It takes thousands of psi and thousands of lbs of force to flex/oscillate a barrel while firing. I've seen people mount m9 bayonets and use them on the end of their rifle to pry things like wooden crates open without "flexing" an m4 heavy barrel.

 

[paul73]

barrel is not flexing by pushing on it with your fingers

Sober up then post.

 

[moojpg2]

Sober up then post.

I don't drink, and you said it yourself in your original post.

I have a head scratching moment here.
Other day while shooting a test, I had a feel examining the rifle that barrel may ( or may not) have too much of a free play inside the hand guard. It does not wobble free, of course, but held between index finger and thumb I could feel it moving up and down that felt as too easy - it should move but I am not sure of for how much. Now, when it is cold, I feel it moves less. It is a 20” heavy barrel, and I am not sure if it supposed to have that much flex.

Nut sits on red loctite most likely and not movable easy. I wonder if I lose my marbles here, or is it a possibility that after 1-2k shots there can be any play introduced in the barrel to upper joint that may warrant the removal and retightening of the barrel nut?
Or am I nuts and it never happens and some play on hot barrel after series of 200 shots is warranted?

Then you absolutely butchered your rifle for no reason...

Ok. Ain’t there an other thing like drunken sledgehammering at precision machinery.

I took the mofo nut off. A 1000F heat gun and some hammer in the end as even maxed out 200lb/ft was not enough to break it free. I broke and cracked nylon upper cradle. Viced it on metal, hammer, and Then it moved.

My respect to LaRue. They mirror polished mating surfaces of upper and barrel.
Of not great news now. With nut off, there was almost 0 horizontal play, but there was a distinct amount of vertical play. I suspect I may be dropped rifle once, who knows.
Sucks.

Anyway, I got nut back at 80 lb/ft. Feel no excessive play now. If I feel like it I may get new upper and swap it out. Does not feel necessary now, but, will see.
View attachment 545805

I'm pretty sure LaRue knows how to install a freaking barrel man. No way that barrel is moving or flexing "between your index finger and thumb."

You're chasing extreme accuracy, I get it, but has it ever occurred to you that maybe those fliers or slightly off groups might just be you, or maybe a slight breeze that kicked up down range, and not the rifle or the ammo? Put the thing in a ransom rest and then get back to us. I bet your groups suddenly tighten up beyond belief. I'm not saying you can't shoot, you've posted some nice targets on here with that rifle, but it is possible that you just aren't always capable of consistently shooting the .5 moa groups you know the rifle is capable of with factory ammo. I also know that if I had a bull barrelled AR that shot .5 moa or better with factory ammo I'd just buy the factory ammo and move on with life because it already shoots better than me on my worst days anyway. The best 5 shot group I ever shot with a .223 is just under 3/8", best I ever did with a .308 is slightly under 3/8" of an inch. On my worst days I know I can almost always squeak out about 1 moa at 100yds prone on a bipod or bags. If the rifle falls consistently somewhere in that range that's as good as I'll ever get so it's certainly good enough for me to compete with.

 

[PappyM3]

Then you absolutely butchered your rifle for no reason...

I'm pretty sure LaRue knows how to install a freaking barrel man. No way that barrel is moving or flexing "between your index finger and thumb."

Yeah, because manufacturers during the past year trying to pump out more product as quickly as possible to meet demand couldn’t possibly have a QA/QC issue pop up. That never happens.

You don’t think it’s possible one of the assemblers used red loctite and then applied too little torque by accident?

The barrel is not flexing by pushing on it with your fingers, no way a 20" heavy barrel made out of stainless or 4150 steel is gonna flex significantly with your fingers,

The barrel flex everyone is talking about here is wiggle at the barrel extension due to a loose fit. “Flex” is used for both actual bending, but also angular movement at the receiver. He isn’t talking about the heavy barrel bending. The flex term is similarly used for free float handguard to denote both bending and also movement due to how it is secured to the barrel nut.

 

[mac1911]

3500 rounds per barrel is not much. I hope mine will last longer, at at least 3/4 moa. But, it is what it is, of course.

Its not much but some of these guys run hot loads and dont wait until accuracy fades.

 

[PatMcD]

3500 rounds per barrel is not much. I hope mine will last longer, at at least 3/4 moa. But, it is what it is, of course.

With a White Oak Wilson barrel, I expect about 3000 rds (1 season of HP) before it'll start to throw fliers at 600 yards. It will still hammer the shit out of a target out to 300yds, but that's not where you lose the game. They will probably go 3500-4000 rds, but I don't want to have to change barrels partway through a season. They are $200-$225 barrels, so one a year is a bargain.
I'm using Bartlien barrel now and expect 6000 rds through it. It's a $400 barrel. So you can see, the cost per rd through a barrel is pretty close. Just a matter of how often you want to swap out barrels.

 

[paul73]

Just a matter of how often you want to swap out barrels

Just curious- what is your approach to swapping uppers? Any specific number of barrels per upper, or it really not that relevant, as long as it is in acceptable shape?

 

[PatMcD]

I know the AMU would use a new upper receiver every couple of barrel changes, but they aren't paying for them out of their own pocket, if you know what I mean. The A4 receiver I'm using has had at least 4 barrels on it. My A2 must have had a dozen on it.
Not a lot of wear areas on the upper.
A new bolt with every barrel wouldn't be the worst idea, but I'll go a couple barrels.

 

[1903Collector]

Is this is reference to the big thread of the barrel nut, or of the threaded connectors the JP handguard uses to attach to the barrel nut?

I went to JPs site and looked at the install instructions for the MKIII hand guard, it specifically calls out Loc-tite 271 for the barrel nut. BTW the JP was probably the hardest free float I have installed with LaRue being the easiest.

 

[jct61765]

How could the barrel nut possible loosen? One of the notches has to be lined up with the gas tube that is installed after the barrel. The tube through this notch would prevent the barrel from loosening to any meaningful degree (probably just a fraction of a degree until blocked by the gas tube). The torque range is pretty wide - 30-80 ft lbs according to the Armalite instructor I took the class from.

Sig Sauer does there's up to 110 ft lbs.