Barrel Extension Separation!

[1075 tech]

The way I understand this, either the pin was sheared or was too short and never was properly fitted locking the barrel and extention together. Which was it?

In my case, the indexing pin was never in contact with the barrel threads. I have heard both that the indexing pin is supposed to go into the barrel and that it is only for indexing into the upper, not for securing the extension to the barrel.

[Wheelhorse]

In my case, the indexing pin was never in contact with the barrel threads. I have heard both that the indexing pin is supposed to go into the barrel and that it is only for indexing into the upper, not for securing the extension to the barrel.

Apparently the pin isn't always fitted into the barrel. The following quote was written by someone who seems to know something about this, found with google:
"Just to be clear, only custom made barrels will have the pin drilled into the barrel.
Production barrels use a 3/16" long pin which ONLY presses into the extension.
These barrels rely only on TORQUE to keep the extension on the receiver.
Of course, at 120-150 ft-lbs, it's not coming apart...

I specifically use a 1/4" long pin so that I can drill 1/16" into the side of the barrel, adding the pin for extra security."

[Wheelhorse]

I wonder if sometimes when setting the headspace, less than recommended torque is used in order to get the correct headspace.
This would certainly speed up production.

[Hansel&Grendel]

Excellent point; hadn't thought of that. Also, 150 ft. lbs. of torque for barrel extension to barrel supports that I sure as heck didn't over-torque the EFAB when clocking it at 10:30-11:00 for final wrenching, ~ 20 ft. lbs., all while using the Geissele RR. For this particular 6.5G build, I used an ALG defense rail with their shim kit; barrel nut torque most likely did not exceed 55 ft. lbs.

For those interested, here is an interesting discussion about barrel extension/barrel separation. Some of the comments were made by people in the barrel manufacturing industry.
https://www.m4carbine.net/showthread...Extension-Help

[A5BLASTER]

Excellent point; hadn't thought of that. Also, 150 ft. lbs. of torque for barrel extension to barrel supports that I sure as heck didn't over-torque the EFAB when clocking it at 10:30-11:00 for final wrenching, ~ 20 ft. lbs., all while using the Geissele RR. For this particular 6.5G build, I used an ALG defense rail with their shim kit; barrel nut torque most likely did not exceed 55 ft. lbs.

For those interested, here is an interesting discussion about barrel extension/barrel separation. Some of the comments were made by people in the barrel manufacturing industry.
https://www.m4carbine.net/showthread...Extension-Help

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.

[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/...ps-techniques/

[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/...ps-techniques/

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.