Build Thread AR15 barrel extension replace

[BlackdogGS]

Have any of you done it? I have a barrel that's a little sloppy and I'd like to tighten it up a bit.

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[DirectDrive]

This question comes up from time to time.
Your barrel was not assembled correctly by the barrelmaker.
The barrel extension is torqued to 150 ft lbs by the barrelmaker and then the gas port is drilled.

The locating dowel on the extension and gas port must be timed to TDC.
If you try to re-tighten an AR barrel extension, it is doubtful that these two key elements will land at TDC.
If it's a cheap barrel, toss it.
Nice barrel, send it back for replacement.

 

[BlackdogGS]

It's a LaRue barrel. Not cheap. It's just a bit loose in the upper, probaby acceptable to most.

 

[DirectDrive]

It's a LaRue barrel. Not cheap. It's just a bit loose in the upper, probaby acceptable to most.

Oh, if I understand correctly, that's a different problem than described above.
Sounds like it's the barrel extension-to-receiver fit.
(you may need to take the handguard off to verify where the movement is)
That's not normal or acceptable, esp. in a rifle like a Larue.

This fit is normally very snug.
Being a Larue, I'd contact them for a return shipping label.
If it is BE to receiver fitment, the fix is to find a receiver that fits your BE.

The Kichen Table Gun Plumber's Union would disassemble and then re-assemble with Loctite Blue on the slip fit areas.
You're using Loctite as a "gap filler" and not a thread locker (no Loctite on the barrel nut threads).
A cheesy fix though, IMO.

Some "precision AR builders" do this "gap filler" thing as a normal routine.
And even go with a weaker Loctite like green or purple....but those break down at 300°F

At least blue goes to 600°F

 

[Boboclown]

probaby acceptable to most.

Not acceptable to anyone. No matter how much a rifle costs, the barrel should not be loose.

 

[HB of CJ]

Same answer as given better before me and thank you. The AR15 or M16 barrel extensions with the locking lugs are installed at the barrel manufacturing place. The old torque value we learned years ago was about 85 pounds. Non user adjustable or removable.

Yep ... the tooling required to R/R the barrel extension is best done by the barrel maker. The head space establishment must be perfect. If the barrel extension slides loose into the upper receiver it might be a dimensional problem with the upper and NOT the barrel.

Ideally that pesky barrel should slip on very tight into the upper. For a perfect build the barrel gets put into a lathe and the extension gently polished for a perfect fight fit. You keep tight combinations for match gun builds.. Certainly it should NOT fit LOOSELY into the upper.

You have a premium barrel? How good is your upper receiver? I for one would just call up both providers and explain your build problems. My guess is it might be the upper receiver precision and NOT the barrel. They SHOULD hand slip tight into each other.

hundreds of builds

 

[BlackdogGS]

Not acceptable to anyone. No matter how much a rifle costs, the barrel should not be loose.

Look at some builder AR YouTube videos. Most barrels slip right in with a tiny bit of wiggle. Very common and acceptable. I was hoping for a snug fit on this one.

 

[Boboclown]

Look at some builder AR YouTube videos. Most barrels slip right in with a tiny bit of wiggle. Very common and acceptable. I was hoping for a snug fit on this one.

The barrel shouldn't be wobbling after the barrel nut is tightened.

 

[BlackdogGS]

I'm talking about the barrel fitting into the upper only. Barrel nut was never mentioned.

 

[Boboclown]

Normally a loose barrel is only a concern if its loose AFTER the barrel nut is placed and tightened.

 

[HB of CJ]

Respectfully ...

Snug fit tight No wiggle room. I have not watched the various incorrect build videos. Well ... I tried to watch one and got as far as the lower roll pin installation. I cringed. Not the way to do it. Wondering now if they used sloppy parts with the barrel extension to receiver fit just to ease and speed up the various bad videos?

I would much rather have a build be tight and require fitting than have that barrel slip easily into the upper. Tolerance drift or stacking is expensive. Nowadays they probably just make all the parts slightly looser? Anyhow that pesky horrible OEM barrel nut should tighten everything up. No slop. A tight barrel. No wiggle.

Now for the screaming. Old School. Not necessarily better but maybe. Barrel torquing. The barrel gets locked down hard. The upper floats. 40-42 adjusted finished torque. You DO NOT go to the next hole. You remove the barrel and gently dress the upper receiver front flat. Re-torque. Over and over. DRY. No lube.

Requires time and knowledge. Not for manufacture build monkeys. They do not have the time. Torquing up that horrible pesky OEM barrel nut is the most time consuming and skill level required part of the home built AR15. No upper receiver glove. Wrong. The gas tube must NOT touch the key. Yikes! Much fun.

This was one reason we got away from the pre staked carrier keys. Wrong also. No key staking. It gives you a little wiggle room installing that horrible OEM barrel nut. The key screws get just kinda tight. When the gas tube fits perfect and there is a test for this, THEN the key screws get torqued up properly. No staking.

PEM me if you want more. The new way. The correct old way. Long ago, far away.

hundreds of builds.

EDITED EXTRA EXTRA EXTRA! Read all about it. If your finished build has a noticeably loose barrel that you can feel wiggle room with flexing the rifle, then it might, (might) be a cracked barrel extension. Remove the hand guards and look. If so, DO NOT FIRE Caused by improper barrel manufacturing. I have seen this.

Thank you Boboclown

 

[BlackdogGS]

From the ultimate AR builder:

Most people use Loctite for this step and it is a lot easier, but...This is the ULTIMATE AR !!! So, we're gonna do it right.

First we get to measure the Inside Diameter(ID) of the upper where the Barrel Extension slides into, then we will measure the Outside Diameter (OD) of the Barrel Extension. Check the Barrel Extension for any burrs or high spots. If the difference is .0025" or less, you are good to go, no need for a shim.



Now we get to do some math.....


Then we make a trip to the local Industrial supply house and get some Stainless Steel shim stock of the correct thickness (in this case .002"). Get a pair of sharp scissors and cut the shim to fit around the barrel extension (make sure it clears the feed ramps). I take a flat stone and knock the burrs off the shim to make it flat again.


Wrap it tightly around the extension, with the seam to the right or left side of the rifle (NOT the top or bottom), secure it with a piece of tape to get it started (remove the tape before you slide it all the way in). I put a drop of blue Loctite in the seam right before I put it all together


You can heat the receiver up a little if it's a little tight getting together.

 

[DirectDrive]

From the ultimate AR builder:

Most people use Loctite for this step and it is a lot easier, but...This is the ULTIMATE AR !!! So, we're gonna do it right.

First we get to measure the Inside Diameter(ID) of the upper where the Barrel Extension slides into, then we will measure the Outside Diameter (OD) of the Barrel Extension. Check the Barrel Extension for any burrs or high spots. If the difference is .0025" or less, you are good to go, no need for a shim.

View attachment 433797

Now we get to do some math.....
View attachment 433798

Then we make a trip to the local Industrial supply house and get some Stainless Steel shim stock of the correct thickness (in this case .002"). Get a pair of sharp scissors and cut the shim to fit around the barrel extension (make sure it clears the feed ramps). I take a flat stone and knock the burrs off the shim to make it flat again.
View attachment 433799

Wrap it tightly around the extension, with the seam to the right or left side of the rifle (NOT the top or bottom), secure it with a piece of tape to get it started (remove the tape before you slide it all the way in). I put a drop of blue Loctite in the seam right before I put it all together
View attachment 433800

You can heat the receiver up a little if it's a little tight getting together.
View attachment 433801

Gaven is so far off the chain with that BS !


As info is gradually released here , this sounds like a home build and not a complete Larue ?
And the wobble is being noticed with the barrel inserted into the upper, but without the barrel nut installed ?

If my guesswork is correct, I'd torque the barrel nut and then check for wobble.

DD
Who has a lifetime supply of AeroShell 33MS if anybody needs some.

 

[Boboclown]

If its loose after the barrel nut is installed then its a cause for concern. Just put in the barrel, install barrel nut, then if its loose something isn't right.

 

[Cameron72]

If there were so much clearance to wrap a shim around the barrel extension I would be looking for a new barrel or upper receiver.

 

[Mygrainman]

Just just because it says Larue on it, doesn't mean it's not out of spec.. There is a NutnFancy video where he bought a Super expensive, and supposedly supper accurate Larue upper... had nothing bit problems with it... sent it back to Larue 2wice before finally figuring it out himself.(gas port was too small)

The pres of Larue frequents the ARF forum and is really kind of a DB at times from what i've seen.. sometimes with a big name, they get a shizz don't stink attitude and become complacent in the QC, and Customer service departments. I avoid LaRue because of what I've seen.

 

[BlackdogGS]

I posted this question on the wrong website.

 

[DirectDrive]

I posted this question on the wrong website.

All snarkiness aside, a better front end description would have helped pinpoint the problem.
If you are still getting wobble after you torque down the barrel nut, your choices have been well-defined :
(assuming this is about BE to receiver fitment)

1) Get another upper that will yield a snug fit with your barrel extension

2) Do the Loctite trick

3) If it's bad enough to need shims, do option #1

 

[Stomper]

Just just because it says Larue on it, doesn't mean it's not out of spec.. There is a NutnFancy video where he bought a Super expensive, and supposedly supper accurate Larue upper... had nothing bit problems with it... sent it back to Larue 2wice before finally figuring it out himself.(gas port was too small)

The pres of Larue frequents the ARF forum and is really kind of a DB at times from what i've seen.. sometimes with a big name, they get a shizz don't stink attitude and become complacent in the QC, and Customer service departments. I avoid LaRue because of what I've seen.

Didn't click, I don't have 2.5 hours available to watch a Nutin' video... sorry!

 

[Boboclown]

I posted this question on the wrong website.

You weren't being clear enough. How loose is it? Does it continue to be loose if a barrel nut is installed and torqued properly?

Telling us its loose without installing a barrel nut isn't telling us much. It can be loose without the barrel nut, but if the barrel nut is installed and its no longer loose then there's no problem. Don't worry about it being loose until after you install the barrel nut and it remains loose.