Barrel Extension Separation!

[Wheelhorse]

I think he's talking about the barrel nut instead of the muzzle device.

"barrel nut torque most likely did not exceed 55 ft. lbs."

[Wheelhorse]

55 ft lbs? Dang that's like ridicules too high amount of torque.

Accuwasher, locktite and time it by hand with less then 10 inch pounds is perfect. I can't see putting more torque on the muzzle then it takes too tighten the barrel nut.

The barrel is a lever. You put 55 foot lbs on the tip there is no telling how much your putting on the extention.

I think he's talking about the barrel nut, not the muzzle device.

"barrel nut torque most likely did not exceed 55 ft. lbs."

[Hansel&Grendel]

A5, it appears that you misread what I wrote. The barrel nut was torqued at no more than 55 ft. lbs. and the EFAB brake was torqued no more than 20 ft. lbs. (if that much). ALG pre-torque band on its proprietary barrel nut tool is 35-55 ft. lbs torque, well within barrel nut torque range.
(Thanks, Wheelhorse)

[A5BLASTER]

A5, it appears that you misread what I wrote. The barrel nut was torqued at no more than 55 ft. lbs. and the EFAB brake was torqued no more than 20 ft. lbs. (if that much). ALG pre-torque band on its proprietary barrel nut tool is 35-55 ft. lbs torque, well within barrel nut torque range.
(Thanks, Wheelhorse)

Yes I missed read it. My apologies.

[LRRPF52]

Whenever doing any type of muzzle device work, you only clamp the barrel in a vice.

The Reaction Rod or similar devices are meant for barrel nut installation, nut muzzle device work.

It makes zero sense to isolate some other part of the rifle other than the barrel, especially the barrel extension, when doing muzzle device work.

Also, per the M4 TDP, you are not supposed to drill and pin the barrel extension index pin into the threads of the barrel tennon. It is a press-fit operation for indexing the barrel and gas port only, not intended to secure the fit of the barrel extension to the barrel, since the torque spec for installing extensions is quite high, well beyond what most people are capable of achieving without a cheater bar and a heavy vice.

In every instance I've seen mention of someone un-torquing their barrel from the extension, it has been doing some kind of muzzle device work without isolating the barrel, with a few exceptions being Radical Firearms 7.62x39 barrels un-torquing just from firing.

I've also addressed the melonite/QPQ process before here where the coefficient of thermal expansion difference between the steel alloy used for the extension and that used for the barrel can create a problem during nitriding if the nitride shop and client are not on the same sheet of music as to materials and processes.

Since nitriding has become so common in the AR15 barrel industry, these issues have been dialed-in by companies that have been around for a while, whereas new entrants to the market looking at new production lines will have to learn this the hard way. Precision Firearms has been providing quality nitrided barrels to the market for the better part of a decade, so if there was a problem on that end, it was a fluke and they'll handle it.

Another thing that gets overlooked is the issue of muzzle devices that impart torque onto the barrel under fire. We had this problem with a certain flash hider when I did testing for a well-known rifle manufacturer over a decade ago. The Smith Enterprises Vortex FH had a RH twist to it, so it could be installed not even hand-tight, but would require an end mill vice and cheater bar to remove after a low round count. The reason it was a problem for us was because of accuracy. Each firing would induce significant torque stress onto the muzzle threads, and affect group sizes on target. It's an awesome FH for low light when reducing flash to a minimum, but there were major accuracy trade-offs we experienced.



These were heavy bolt rifles with Krieger barrels that were capable of 1/4-1/2 MOA without the Vortex FH. I think we were seeing groups open up to 1.5" or more.

Every variable needs to be accounted for when you change something. Looking at the EFAB, I'm not seeing the kinds of shaping that would contribute to torque, but I'm also not ruling it out.

Either way, using the Reaction Rod to remove the device would contribute to un-torquing the barrel from the extension, provided you exceeded the torque value at the barrel tennon/extension mate-up.

[phishfood]

The physics might be different for flat/straight threads, but I have run into similar issues with tapered pipe thread before. Tighten one end into a fitting pretty dang tight, then tighten a fitting onto the other end just kinda sorta tight. Then have to remove the looser fitting for some reason, and the pipe spins out of the fitting on the other end.

[Hansel&Grendel]

LRRPF52, I always learn from your posts. You and the Rifle Editor for Shooting Illustrated turned me on to the 6.5G. Regarding your comment for clamping of the barrel for brake install/removal, here's where I'm confused as this is off the Geissele website for their Reaction Rod:

"The 556/223 Caliber Reaction Rod makes the removal and installation of barrels, flash hiders, gas blocks and hand guards much easier and simpler. The Reaction Rod is designed to be gripped in a bench vise so that the rod is either horizontal or vertical. The upper receiver is then slid onto the rod and the rod?s integral splines enter the barrel extension and secure the barrel extension from turning. This allows all the torque from barrel nut wrenches to go directly into the barrel extension. In contrast, receiver vise blocks transmit the turning force into the aluminum receiver, a good part of which passes through the small, easily distorted receiver index pin" (emphasis added).

As emphasized the install/removal of flash hiders (and assuming other muzzle devices) are said to be enabled by the Geissele Reaction Rod per their reasoning. Also, having clocked the EFAB with peel washers at 10:30 - 11:00 for a likely torque value not to exceed 20 ft. lbs., was it still possible to un-torque the extension from the barrel? I did not have to use much force when I removed the EFAB, i.e., assuming that it was pretty much equal to the approximate 20 ft. lbs. torque to install the EFAB. And, yes, I agree with your comments about PF and Mark (and his lovely wife).

EDIT: Well, here's a Shooting Illustrated article by Rifle Editor Steve Adelmann regarding muzzle device installation/removal. Over-torque (which I know that I did not do) can separate the barrel from the barrel extension when using a reaction rod or similar device. As Steve and LRRPF52 state, the best way to install/remove a muzzle device is to clamp the barrel in a vise near the work being performed, as pictured:
https://www.shootingillustrated.com/arti...echniques/

[A5BLASTER]

LRRPF52, I always learn from your posts. You and the Rifle Editor for Shooting Illustrated turned me on to the 6.5G. Regarding your comment for clamping of the barrel for brake install/removal, here's where I'm confused as this is off the Geissele website for their Reaction Rod:

"The 556/223 Caliber Reaction Rod makes the removal and installation of barrels, flash hiders, gas blocks and hand guards much easier and simpler. The Reaction Rod is designed to be gripped in a bench vise so that the rod is either horizontal or vertical. The upper receiver is then slid onto the rod and the rod?s integral splines enter the barrel extension and secure the barrel extension from turning. This allows all the torque from barrel nut wrenches to go directly into the barrel extension. In contrast, receiver vise blocks transmit the turning force into the aluminum receiver, a good part of which passes through the small, easily distorted receiver index pin" (emphasis added).

As emphasized the install/removal of flash hiders (and assuming other muzzle devices) are said to be enabled by the Geissele Reaction Rod per their reasoning. Also, having clocked the EFAB with peel washers at 10:30 - 11:00 for a likely torque value not to exceed 20 ft. lbs., was it still possible to un-torque the extension from the barrel? I did not have to use much force when I removed the EFAB, i.e., assuming that it was pretty much equal to the approximate 20 ft. lbs. torque to install the EFAB. And, yes, I agree with your comments about PF and Mark (and his lovely wife).

EDIT: Well, here's a Shooting Illustrated article by Rifle Editor Steve Adelmann regarding muzzle device installation/removal. Over-torque (which I know that I did not do) can separate the barrel from the barrel extension when using a reaction rod or similar device. As Steve and LRRPF52 state, the best way to install/remove a muzzle device is to clamp the barrel in a vise near the work being performed, as pictured:
https://www.shootingillustrated.com/arti...echniques/

And this is why I use the accuwasher system. No torque and a lil locktite it's good and I can take it back off by hand with a 4 inch long pair of channel lock plyer's while holding the rifle/upper in my other hand.

[41bear]

And this is why I use the accuwasher system. No torque and a lil locktite it's good and I can take it back off by hand with a 4 inch long pair of channel lock plyer's while holding the rifle/upper in my other hand.

^^^^^^^ What he said!

[c3k]

In my thread (not trying to hijack this one!), the way my barrel came out of the extension is exactly the same. And, yes, I used the accuwasher system on my muzzle device. The torque I used was minimal.

I'm not sure if our two issues have anything related (production methodology, supplier, etc.), I'm just posting to add a datapoint.

[Hansel&Grendel]

Appreciate your post. The build referenced here was 2017; I've since switched to the Accu-washer system as well for greater ease. I don't see where 20 ft. lbs. of torque to install/remove a muzzle device would undo 150 lbs. of barrel extension/barrel torque. As LRPFF52 notes, issues can occur with the nitriding process. Or, torque was not proper with the barrel extension and barrel to begin with. PF is taking care of the issue to their credit.

Regardless, I have since modified muzzle device install/removal to only clamp the barrel in a vise (with soft jaws or something similarly suitable). I actually have a portable vise platform wherein I can still use a reaction rod while also clamping the barrel with a main vise -- yes, overkill, but it secures everything rock solid at both ends.

[LtDan]

If I understand things correctly the alignment pin goes through the barrel extension into the barrel threads, thus pinning it from movement.
So either the pin was sheared or it came loose? (backed out of the divot in the threads)

No the extension alignment pin does not lock into the threads on a AR

[PrecisionFirearms]

I going to jump in on this one. This barrel was produced probably 4 years ago before we discovered that the nitriding process can reduce the torque required on the barrel extension. For the past 3 years to there abouts we send the barrel to nitride before installing the barrel extension and drilling the gas port.

Using a reaction rod seems to aggravate the situation. Barrels that would probably last for 1000's more rounds are being loosened by this method. We used to use the Reaction rod in our shop quite a bit until we had this happen on several barrels in one week from several different manufacturers. Most of these were from suppressor attachments that were rock set on. We now use another system that works better.

The extension pin is for alignment only.

Its not simply a deal where we can reinstall the pin because re torquing will place the timing of the alignment pin and the gas port about 5 to 10 degree off. We have to go through our batch of extension and try to find one that will match the barrel. Being the barrel is nitrided we cant just recut the chamber by .005 to match the gas port.

Unfortunately in this barrel's case none of the 100 extension we have in house clocked at the right place so we need to wait for the next batch of extensions next month to check if any of those will fit. If not we will discard the barrel and replace.

Mark Hostetter
Precision Firearms

[Kswhitetails]

Mark, educate me. I have always been under the impression that the barrel extension has the hole drilled after it's installed and torqued to 150ft-lbs, or whatever the spec is. Then, the index pin hole, and the gas port are drilled on a fixture ensuring they remain exactly in-line. That way the indexing happens easily and without timing issues. Am I wrong here?

I can see how the thermal and chemical properties of nitriding a barrel with an already installed extension could cause expansion/contraction loosening. But those lessons have been learned since nirtiding has become more mainstream, right?

I'm confused how a RR could cause the extension to come loose if the torque required to remove a muzzle device is less than 100 ft-lbs (which is friggin hard to do on a RR; like Grizzly Adams hard), especially considering super max MD torque should be 60 ft/lbs...

Now, rock-set is a different animal; and anyone using it should already know that it is intended to be a permanent fixture. It's like using the two part putty... Don't expect to get away with getting it apart. It can be done, but using it makes you the permanent owner of the two parts and their marriage. Don't go complaining when it doesn't come apart without damaging one or both of the two parts... Question then, why don't we rock-set the extensions onto the barrels?

If you've moved away from the RR, what have you found to be a better solution? I've been eying some bench top barrel vises.

[PrecisionFirearms]

The hole in the extension is drilled to be timed with feed ramps. I think you can figure out why that is important.

Yes it has. Which is why I explained how we are doing it differently now. Out of a thousand barrels we probably only saw this type of failure like 10 times

Only a problem if the extension is torqued to 125 LBS. But Ive seen this happen even on Name Brand Barrels that start with D and B.....Especially with Suppressor mounts and locktite.

You probably could use Rockset. We use red locktite here.

We make a vise block with a accessory Picatinny Rail block that works very good. I have one unit here that has been part of the assembly process on at least 50,000 uppers.

[grayfox]

Footnote guys: on Rocksett, I have used it successfully and also disassembled it successfully and used the parts again. There's a trick to it, suspend the piece with the rocksett portion submerged in water -- boiling or at 200+ deg, for 20-30 minutes, it will come apart like silly putty. It is a silicate type compound that crystallizes, that's what makes it "permanent" but will dissolve in hot water. Heat alone will not faze it as the crystalline structure goes to IDK 2000 deg or so...
But let the hot water seep down to it and bingo!

[FRB6.5]

Rocksett should also come apart with the same amount of torque used to tighten it. It isn't meant to be 'permanent' like red loctite. There does seem to be a lot of misinformation that 'red' = high temp. There is also blue loctite that has the same temp rating as red but comes apart at the same low torque rating you'd expect with a "medium" strength thread locker.

Sadly the more exotic ones listed aren't available at your local hardware store.

https://henkeladhesivesna.com/henkeldocs..._Links.pdf

[Hansel&Grendel]

Footnote guys: on Rocksett, I have used it successfully and also disassembled it successfully and used the parts again. There's a trick to it, suspend the piece with the rocksett portion submerged in water -- boiling or at 200+ deg, for 20-30 minutes, it will come apart like silly putty. It is a silicate type compound that crystallizes, that's what makes it "permanent" but will dissolve in hot water. Heat alone will not faze it as the crystalline structure goes to IDK 2000 deg or so...
But let the hot water seep down to it and bingo!

This. I've used this method once before on a buddy's personal Mk 18 after talking with the onsite armorers for the State Department DSS/MSD. They oversee hundreds of thousands of rounds in a short period and barrel swap on a regular basis. For removal of a Rocksett muzzle brake, they recommended boiling water, turning off the flame and then soaking the muzzle end of the barrel while occasionally rotating it in order to render the Rocksett pliable. After just under 10 minutes, I used a 1/2" drive 24" breaker bar and was pleasantly surprised at how easy it was to remove the muzzle brake.

[PrecisionFirearms]

We use the boiling water method too.
Works well most of the time.