How to put a barrel extension on a barrel

[Bodhi275]

So, I'm excitedly ready to put on my new Turbo Suppressor and took the A2 Birdcage off, no problem. But to do this, I took the barrel out of the upper as I didn't have an action bar... yet. I go to reinstall the barrel and slowly go to torque down the barrel nut with 15 ftlbs. and the nut slips and goes too far. Like, I can turn it by hand.
I disassemble it and find that the barrel extension guide pin is gone. Also note, that I bedded the barrel with green Loctite and now can't get the old barrel extension off the upper.
I order a new barrel extension and it looks great. But when I place it on the barrel and snug it down with my hand, it turns past 12 o'clock by just a few degrees and now doesn't index properly with the gas tube. And, this is where the screw-ups accumulate:
1. I used red Loctite on the barrel threads
2. Used a hot air gun to loosen the red Loctite, but the pretty stainless steel is now dark yellow to blue'ish/purple
Did I screw up the temper on the extension?
3. How do you lock down the barrel extension at the 12 o'clock position and timed with the gas tube but be tight on the barrel?
Do I use the guide pin to "stake" the extension to the barrel?

Sure could use some guidance/experience here...

 

[BravoSierra]

Pictures? Large frame or small frame AR? Assuming an AR, assemblers don't mess with extensions 99.9999% of the time unless they happen to be machinists too and want to do the whole thing themselves. Because if it is indeed the extension you sheered off, unfortunately you're going to want to send it off to a smith. How attached are you to the barrel? May be cheaper to get a new one.. Better yet, get the whole project to a smith at this point and see what they say. And Don't use loctite on a barrel install. 30ft-lbs value to start with, and that value is with mil spec anti-seize after stretching the threads a few times, no threadlocker of any kind on the reciever threads.. but yeah, a smith should be in your near future with this.

 

[x248716x]

well, hopefully, you don't bed the barrel with loctite ever again, despite what the folks say that swear by it. SMH.

you said the BE guide pin "is gone"? where dafuq did it go, it didn't simply vanish into thin air. Is the notch on the upper receiver buggered?

putting a new BE on your barrel, you have 2 things to resolve, and they don't go hand-in-hand and resolve together. You already discovered one of them, when the new BE is on the barrel, the gas port is now somewhere other than TDC. You may need to plug the old gas port, and drill a new one, precisely located.

you also have to verify headspace, and that the bolt lugs will, first of all, fit and rotate, and that it is a snug fit, and also that the barrel + BE combo headspaces correctly on a GO gauge, and a NO-GO gauge. Actually, you have to do the BE headspace resolution first, before you address the gas port timing. And I woulda used the red loctite on the barrel threads to the BE, only after you've verified headspace, and it's the final, never-looking-back, point-of-no-return, massive torque applied final assembly. This is one point where the AR-15 is no longer a Lego assembly.

so it goes to the earlier comment, how valuable is this barrel? is it more than, say, $500, or is it a Bear Creek 30% sale clearance barrel? if it's a cheap barrel, then you now have a paper weight, but you learned some valuable lessons, so that's a plus. If it's an expensive barrel, unless you're able to do all of this yourself, then this barrel is going to a gun smith. as astutely mentioned above by BravoSierra.

 

[msgriff]

The index pin is not intended to connect the barrel tenon (threads) to the extension. The barrel is clamped and you use a barrel extension wrench to torque the extension to 150-175 lb-ft dry. Your headspace may also change and could then become out of spec. Distance between the front of the bolt lugs and the barrel tenon can also change. You then weld closed the old gas port and drill a new one, which needs to be perfectly aligned with the index pin. There are some WECSOG hacks, like shimming the tenon, DIY extension wrench out of an old bolt, strap wench on the extension and say "click-click", letting the gas block seal the old port while aligned with the new gas port, stuff like that. Or just buy a new barrel.

ETA: Barrel extension wrench for use with a torque wrench:

 

[Constructor]

Or just buy a new barrel.

Everything else needs to be done by a real smith, most can't install a new extension or don't have 100 to try until one lines up perfectly with the old gas port. Sometimes it takes an hour to find one close then we face the extension a thou or 2 until it lines up and headspace is correct. In the end it will be cheaper to buy a new barrel.

BTW whatever company you purchased the barrel from did not torque the barrel extension correctly or you wouldn't be able to get it off. I don't think I would buy another from the same manufacturer, it's likely they install all extensions the same way. If The extension was Nitride/melonite treated (black) that could be the reason it was loose.

 

[Bodhi275]

well, hopefully, you don't bed the barrel with loctite ever again, despite what the folks say that swear by it. SMH.

you said the BE guide pin "is gone"? where dafuq did it go, it didn't simply vanish into thin air. Is the notch on the upper receiver buggered?

putting a new BE on your barrel, you have 2 things to resolve, and they don't go hand-in-hand and resolve together. You already discovered one of them, when the new BE is on the barrel, the gas port is now somewhere other than TDC. You may need to plug the old gas port, and drill a new one, precisely located.

you also have to verify headspace, and that the bolt lugs will, first of all, fit and rotate, and that it is a snug fit, and also that the barrel + BE combo headspaces correctly on a GO gauge, and a NO-GO gauge. Actually, you have to do the BE headspace resolution first, before you address the gas port timing. And I woulda used the red loctite on the barrel threads to the BE, only after you've verified headspace, and it's the final, never-looking-back, point-of-no-return, massive torque applied final assembly. This is one point where the AR-15 is no longer a Lego assembly.

so it goes to the earlier comment, how valuable is this barrel? is it more than, say, $500, or is it a Bear Creek 30% sale clearance barrel? if it's a cheap barrel, then you now have a paper weight, but you learned some valuable lessons, so that's a plus. If it's an expensive barrel, unless you're able to do all of this yourself, then this barrel is going to a gun smith. as astutely mentioned above by BravoSierra.

The guide pin was lost for a bit, but found. Turns out that when I applie the 15 ft lbs of torque, the pin just pivoted out. Notch is fine, barrel is fine. Just now seem to have a permanent extension in the upper.

 

[Bodhi275]

Everything else needs to be done by a real smith, most can't install a new extension or don't have 100 to try until one lines up perfectly with the old gas port. Sometimes it takes an hour to find one close then we face the extension a thou or 2 until it lines up and headspace is correct. In the end it will be cheaper to buy a new barrel.

BTW whatever company you purchased the barrel from did not torque the barrel extension correctly or you wouldn't be able to get it off. I don't think I would buy another from the same manufacturer, it's likely they install all extensions the same way. If The extension was Nitride/melonite treated (black) that could be the reason it was loose.

Okay, okay... hold on tight... this was part of an upper of my first AR build (about 10 years ago) and the upper was from Palmetto Armory. I don't think I spent even $400 on the whole upper. When I looked at the barrel, minus the extension, it looked like the index pin was staked into the threads, hence one of my previous questions.
Sad part is that before all of this, I had this thing dialed in and was definitely a good shooting rifle. Thought, "...all this needs is a suppressor!". But when I started taking this portion apart for the first time, things just compounded.
I think most here are right and I just need to get a new barrel.

 

[Constructor]

That extension should be torqued to 150ft pounds, the alignment pin is only to align the gas port straight up so the gas block will be straight up and the extension lugs will mate with the bolt lugs. Normally the barrel extension is installed, alignment pin installed then the gas port is drilled inline with the pin.
Either me or one of my guys have installed over 70,000 barrels extensions from 2012-2017, after installed we can't get them off even with an impact.
What color is the barrel extension...black? Most likely Nitride treated on the barrel. When the barrels and extensions are nitride treated together the extension expands and loses torque regardless of what L&M metals says, they told me the same thing in 2012. I guess I shouldn't expect anything different from someone trying to sell me something. Watch this clip- I can hold the barrel in my bare hand and remove the extension after nitride treatment by L&M metals. After I installed new extension and torqued them correctly we could not/can not get them off without cutting a slot down the side of the extension. You can see the newly installed silver extensions in the background.

 

[msgriff]

Are you, at this point, only concerned about removing the stuck barrel extension and salvaging the upper?

 

[x248716x]

lots of good technical information in this thread.

 

[Bodhi275]

That extension should be torqued to 150ft pounds, the alignment pin is only to align the gas port straight up so the gas block will be straight up and the extension lugs will mate with the bolt lugs. Normally the barrel extension is installed, alignment pin installed then the gas port is drilled inline with the pin.
Either me or one of my guys have installed over 70,000 barrels extensions from 2012-2017, after installed we can't get them off even with an impact.
What color is the barrel extension...black? Most likely Nitride treated on the barrel. When the barrels and extensions are nitride treated together the extension expands and loses torque regardless of what L&M metals says, they told me the same thing in 2012. I guess I shouldn't expect anything different from someone trying to sell me something. Watch this clip- I can hold the barrel in my bare hand and remove the extension after nitride treatment by L&M metals. After I installed new extension and torqued them correctly we could not/can not get them off without cutting a slot down the side of the extension. You can see the newly installed silver extensions in the background.

Wow! Great info! Yes, the BE is also Nitride treated.

 

[Bodhi275]

Are you, at this point, only concerned about removing the stuck barrel extension and salvaging the upper?

I'd like to salvage the upper if possible, but I haven't much hope. I went ahead a bought an AP M4 upper to replace it and a new BCM barrel, too.

 

[Constructor]

I've been telling people about the problems with nitride treating bolts and extensions since 2012 but they all think they know better and keep doing it. They will all come apart sooner or later and the lugs will compress increasing headspace. Good for them that their warranties only last a year or 2 or they would be replacing a lot of barrels.

 

[Bodhi275]

The guide pin was lost for a bit, but found. Turns out that when I applie the 15 ft lbs of torque, the pin just pivoted out. Notch is fine, barrel is fine. Just now seem to have a permanent extension in the upper.

I'd like to salvage the upper if possible, but I haven't much hope. I went ahead a bought an AP M4 upper to replace it and a new BCM barrel, too.

SUCCESS! I was able to bang out the BE without damaging the upper. Upon closer inspection, it looks like the index pin sheared off when I applied the 15 ftlbs o'torque.
If nothing else, this was an exercise in which Loctite does what and how to counter act it. And, to be very judicious in when and where to apply it. ; )

 

[Bodhi275]

I'd like to thank Snipershide and the posters to this thread for such quick and thorough responses. It's like the software I use in my day job: I was only taught how to use it when everything is working. But, how I got good at it was breaking it in ways no one expected. Guess gunsmithing is like that, too.
Again, much appreciation for the lessons!