AR-15 Barrel Installation

[Lone star Shooter]

I just received my 6mm ARC barrel. The gunsmith recommends using Loctite 609 (green) on the barrel extension before installing in the upper receiver. My barrel and receiver have an interference fit, so I’ll heat the receiver and freeze the barrel before putting them together. Is the Loctite 609 still necessary? Will the Loctite 609 prevent disassembly?

 

[charnicus]

You get some differing opinions I’m sure but I wouldn’t use the Loctite. Especially if you have an interference fit already. Aeroshell on the extension and be done with it.

 

[mheimer_45]

Use red and be done with it.

 

[Strykervet]

Use red and be done with it.

Just use nothing then. Red won't handle that kind of heat. There's a reason for the green.

It's not a threadlocker, it's for mating two dissimilar types of metal together and can withstand more heat.

Yeah, it'll be a permanent installation. I do this with nice barrels and consider the upper disposable. I also face the upper with a tool to grind it flat.

If you gotta fuck with heating it up prior to installation then there won't be any room or any need for the loctite. I got one of those goddamn things one time and didn't know why I had to use a rubber mallet to seat the fucking barrel. Never again. I guess they're fine if you know that to begin with though, just not my cup of tea.

MUR1 and green loctite and call it a day. OR if you wanna be able to take it apart then CLP or grease. I can't recall offhand and don't feel like digging it up but the armorer manual called for lithium grease I think.

 

[supercorndogs]

It only takes 250F to break down 609. Its not really "permanent." It is also says on the bottle "augments press fit." I.E fills the gaps in a press fit if you have any.

 

[BiggBeans]

Use JB Weld and be done with it

 

[mheimer_45]

I use red after I surface the face. And spread it around the receiver. Red has a breakdown temp of 450*vs green at 200*. I use it on all of my muzzle devices and have yet to have it break lose when removing a suppressor.

 

[mheimer_45]

Just use nothing then. Red won't handle that kind of heat. There's a reason for the green.

It's not a threadlocker, it's for mating two dissimilar types of metal together and can withstand more heat.

Yeah, it'll be a permanent installation. I do this with nice barrels and consider the upper disposable. I also face the upper with a tool to grind it flat.

If you gotta fuck with heating it up prior to installation then there won't be any room or any need for the loctite. I got one of those goddamn things one time and didn't know why I had to use a rubber mallet to seat the fucking barrel. Never again. I guess they're fine if you know that to begin with though, just not my cup of tea.

MUR1 and green loctite and call it a day. OR if you wanna be able to take it apart then CLP or grease. I can't recall offhand and don't feel like digging it up but the armorer manual called for lithium grease I think.

And why the fuck are you taking it down? It’s cheaper just to buy another.

 

[S197]

Use red and be done with it.

There is a Hugh difference between 200 series loctite and 600 series. When you have to use heat to fit a barrel, retaining compound is not needed. You can try, it will not hurt anything but it will create a mess.

 

[whatsupdoc]

NO reason to use any adhesive in an interference fit barrel extension.

 

[bfoosh006]

For the OP ....

It is entirely up to you. Personally I would do it... my previous results make me biased.

FWIW... Loctite sells "LOCTITE 620 is a high strength, high temperature resistant retaining compound." Good up to 200 degrees Celcius.

I believe 609 is recommended since you could heat the upper and more easily remove the barrel if needed.
I have used 609 on numerous uppers and barrels... many hundreds and hundreds of rounds later , no issues.

NOTE... my test involved lapping the upper receiver face "true" , making sure of a snug fitting upper to lower, smooth gas tube interface to the gas key, and using the 609 Loctite.

And my results were improved precision... not with every single brand ammo, but more then enough to make a believer out of me.
Some of the improvements were flat out dramatically better.... much smaller groups, and certainly more consistent groupings.

I swear there were less flyers.... but my less then scientific recording and average Joe testing certainly couldn't stand up to a court of law, Lol

Criterion Barrels has a video series on the "

Criterion Barrels Releases “Accurizing AR-15” Video Series​

Part 3 , at the 50 second mark, shows them using the Loctite 609.

https://criterionbarrels.com/media/accurizing-the-ar-15-video-series/?v=00dc5da36527

All that said, SS shims and thermal fitting can produce snug fitting barrels.
I also strongly suggest lapping the upper receiver face... the video shows what I mean.

Ultimately... do as you see fit with your rifle.

For those interested... ( pardon the poor writing skills and presentation... I am not a writer... I am a mechanical guy, and work with my hands. )
PSA OEM 20" Barrel before and after the Assm. tricks
https://www.ar15.com/forums/industr...-gas-upper-review--PSA-Nailed-it-/301-285762/

My best group to date from my 6.5CM 22" Criterion barreled PSA upper and lower. Shows the barrel can out shoot me. ( The flyer is my fault 100% ) 10rds Hornady 140gr AG , 100yds , scoped, benched .. etc.
Assm. tricks listed above used.
Yes, Cherry picked... I am proud of the group.

FN 308 CHF CL Barreled, PSA upper and lower , same assm. tricks. ( second photo ) 10rds 155gr Hornady AG, same bench shooting

 

[zerolumens]

^^ thanks for the info above. was interesting to see someone elses approach to building an upper.

 

[Precision Underground]

You probably don’t need it with a thermal fit but I do it anyway. I picture it as more of a damper for harmonics in that case. Maybe the thermal fit is on 2 points and not all the way around the full circumference of the extension. In that case the 609 will fill the gaps and make vibrations more uniform. That’s how it works in my head anyway. Either way it’s easy to do and if you don’t put too much it doesn’t make that much of a mess.

 

[drewthebrave]

You probably don’t need it with a thermal fit but I do it anyway. I picture it as more of a damper for harmonics in that case. Maybe the thermal fit is on 2 points and not all the way around the full circumference of the extension. In that case the 609 will fill the gaps and make vibrations more uniform. That’s how it works in my head anyway. Either way it’s easy to do and if you don’t put too much it doesn’t make that much of a mess.

Agreed. It may not be necessary, but a dab of 609 or 620 can't hurt. Anything to reduce the amount of play is worthwhile in my book. Think of it as cheap insurance to get the most out of your build.

 

[Yondering]

Agreed. It may not be necessary, but a dab of 609 or 620 can't hurt.

Actually it can, and I'm pretty sure nobody recommending it for a heated interference fit has actually done it.

The reason - the combination of heat and a tight fit (at least with the various popular greens - 609, 620, and 680) results in an almost immediate cure, often before you can get the part fully seated. These adhesives are not designed for a high temp installation; they can handle all the temp a barrel extension will see in a semi-auto once they're cured, but assembly at high temp is a different thing entirely.

If you have a true interference fit, you don't need or really want any Loctite in there. Metal to metal contact is good to go for that kind of fit. Of course if it's just a firm sliding fit or anything looser, absolutely use green Loctite. 680 is my preference.

 

[Yondering]

I use red after I surface the face. And spread it around the receiver. Red has a breakdown temp of 450*vs green at 200*. I use it on all of my muzzle devices and have yet to have it break lose when removing a suppressor.

Sorry but anyone talking about "red" or "green" like they're just one thing doesn't know a quarter as much as they think about Loctite and it's applications. Go look up what temp green 620 is rated for.

It's really too bad we can't get more people here to save their advice for things they actually know.

 

[drewthebrave]

The datasheets for these show detailed graphs about the strength of the bond at different temperatures, and it's more of a gradual curve of diminishing strength rather than "it's good at this temperature, then it fails". But here's a general rule of thumb temperature rating for these:

Loctite 620 = 400F
Loctite 609 = 300F
Loctite 680 = 300F

I've used 620 and 609, and haven't noticed a difference. I'm not dumping mags, and my use case may not represent yours. If you're not using your barrel as a pry bar or hammer, these will probably all work just fine.