I've done plenty of these on M16 series rifles for the military. Everytime with the T.O. out in front of me. The most trouble I've had is getting everything lined up while staying withing 30-60 ft lbs.

Well, I'm trying to install a Rainier Ultramatch .308 barrel on my M5 upper and things went wrong. I don't know how though. I was using upper blocks in a vice. I was using a calibrated SnapOn torque wrench. Installed never exceeding 60 ft lbs, but the alignment pin broke and the barrel spun. Rail is a 15" MI MLOK. I've gone over every conceivable thing to find out what I've done wrong, but can't come up with anything. Used grease, tightened down and loosened three times before I attempted final tourque and alignment, etc.

Any thoughts?

Thats odd. I did that twice in a row but I had the barrel clamped in, not the receiver. Seems like a problem with the barrel extension.

I'm not the type who immediately jumps up and down and hollers about crappy parts when something goes wrong, but I seriously can't figure out how I did this.

Sounds like bad barrel extension. Don't see how the aluminum receiver would break a steel alignment pin.

Is the pin just snapped off, or is there some distortion at the break?

If its a clean snap, with a granular appearance, the pin is faulty.



I would be looking at the pin very closely.



Shearing a steel pin in this application just does not make any sense.



Sometimes dowel pins can get over hardened, or not properly tempered,

making them very brittle.

Even a mild steel pin should not shear in this application.



IMHO YMMV

Murphy's law just kicked in, stuff happens.

Nothing wrong in reviewing your techniques and practices, keeps you sharp. Every once in a while, a bad part slips on in.

I thought there was going to be a reaction rod mentioned in the op, but surprised when it was not involved. Chalk it up to a bad pin...

Has there been similar incidents with the use of a reaction rod?  I was thinking about getting one, maybe not now that I'm reading this?

Regarding the original issue, hard to believe but it can only be a bad pin.

There have been some threads on the issue, but the jury is still out on the absolute best way to mount the barrel. I don't want to hijack the op's thread.

The op used a method that has been tried and true and had a weird failure of the index pin...I think there would have been an issue with that failed part any way you get the job done. Sometimes stuff happens.

Sometimes funky stuff happens. The index pin may have just had a bad heat treat. It's one of those "Don't think too much into it" type of things.
Contact the vendor on Monday.

Sucks. I've been waiting for months to collect all the parts for this rifle and I was fired up to have a rifle I could shoot. Now I've gotta fight CS to get my barrel extension fixed...

From what i understand rainer has great CS, hope it goes well.

Brother, let me tell you, I have been there.  I spent a year working on building up a Mega .308 only to have it not shoot worth a damn.  Reliable as hell but about as accurate as a Red Ryder at 100 yards.  In fact, I'd give the edge to the Red Ryder at that distance. Let me tell you that I spared NO expense on this gun.





Turns out that the ( new type ) Wilson gas system I was trying out was butting against the inside of the carrier key ( despite my best efforts to make sure that wouldn't happen ) AND the APEX handguard was ALSO binding against the OD of the tube.  Despite turning the tube down at that point AND shortening the interface at the key I could only get so much wrung out of the gun.





Just spent SEVERAL hundred dollars ordering a whole new gas system, JP handguard....etc, etc, etc.......





ETA:  Holy cats....I just found my old thread in the archive and you and I were discussing JP/Kreiger, etc.....



DAMN MAN!  NOW I AM EXTRA BUMMED FOR YOU!!!  That being said....again...you are not alone!!!!





 

MOTHERFUCKER!!!!!

Got my barrel back today. Get done with dinner and gather everything up to install the barrel. I'm going S L O W trying to do it all right. Get everything shored up in the vice. Grease the threads, run the barrel nut down tight and back it off 4 times. Tourque to 50 ft lbs and start to add little bit of tourque at a time lining up for the gas tube. Get alllllmost to 60 ft lbs (mfgr max spec for Midwest Barrel nut) and POP! alignment pin sheared off again! What in the actual fuck!!!!

FUCK!

The reaction rod holds the barrel itself in place (by the extension), so it doesn't put stress on the receiver or alignment pin lie upper vice blocks do. Not saying it wasn't a combination of a bad pin/assembly procedures, but an upper vice block is not the ideal tool to torque on a barrel nut.

ETA: If the pin came all the way out, just get a new one and tap it in place.
If it sheared off, CAREFULLY drill the rest of it out and install new pin.
In either case, reinstall it with a reaction rod.

I'm just awed that 60 ft lbs broke the alignment pin...AGAIN!

I've torqued up to the Techinical Order spec of 80 ft lbs on M16/M4's numerous times and never broken an alignment pin.  I've broken two alignment pins on this barrel, back-to-back, torquing to 25% less tourque. How in the fuck can 60 ft lbs break a steel alignment pin in an aluminum upper (using delrin upper blocks on top and pinned on bottom) with no noticeable damage to the upper other that scoring on the inside from where the pin spun? I'm so fucking frustrated right now...

I feel your pain, and I'm sure there will be people along shortly to debate my opinion about the reaction rod. I may be wrong and it is just my opinion, but the rod doesn't flex like the vice block and upper do, and it keeps the barrel extension/pin stationary.

So did it shear off or come completely out?

Sheared. Just like the last one.

I'm beginning to think you might have a very rough finish on the inside of your barrel nut, or your barrel nut is somehow binding/seizing on your barrel extension, and this is placing extraordinary stress on the barrel extension which is rotating in the receiver.

What kind of barrel nut are you using?

The best thing is to place grease on the surface of the barrel extension that faces the barrel, and to NOT have any grease on the face of the receiver and the back of the extension.  This allows maximum friction between the receiver and the extension, and minimal friction between the nut and extension, which is what causes excessive rotational torque.

Flex has nothing to do with this.  This is rotational torque caused by the barrel nut rotating and creating friction with the barrel extension, which puts rotational torque on the extension which is stopped in place by the receiver slot and extension pin.

A reaction rod changes nothing here.  The same rotational torque exists, and the pin to receiver is still the same interference that stops that rotational torque.

Here's what I think is happening..could be out to lunch, but hear me out.

There is a possibility that the ID of the threads on the barrel nut are too tight, or the indexing pin is too long.

I've seen this happen before from manufacturers who just stuff stock into the pin hole, grind it off until they're satisfied, and call it good.

I've had to clean those types of pins up before, and make them pretty before installing.  You can troubleshoot this by looking at the barrel from the front and rear and seeing if the pin is taller than the barrel extension flange/ring.  If so, they need to come down.

I've seen this even from barrel makers that are highly renowned.  This is one of the other myriad of details that gets overlooked by the after-market with AR15's.  With .308's, all bets are off.

The next possibility, and I really hope this isn't the case, is that someone had their assembled barrels nitrided with the extensions and pins already installed.  There are a lot of shops out there sending out barrels for nitriding that don't know what they are doing, and I've seen first-hand evidence of this already.  They see nitriding becoming popular, jump on the bandwagon, with limited/no understanding of metallurgy, then wonder why extensions come loose, feed ramps crack off like obsidian, or caustic salt residue eats the finish in the packaging because it was never washed thoroughly.

ETA: All my experiences with Rainier have been top notch, so I would expect a solid barrel from them, but still verify.  They have always taken care of me.

Agreed. Or that the hole for the pin isn't right so it's pushing the pin up too high.

Sheared, no, come out, yes.  I was having a hard time screwing on the barrel nut and it felt very gritty, like something was cross threaded and eating on the threads.  I backed off and the pin was loose and it looked very chewed up.  No way the barrel nut chewed up the pin so I am not sure how, when, or where it happened.  I plopped it out (it literally fell out) and tapped in a new one.  Done, right as rain ever since.

My thoughts are that it is either a problem with the pins they're sending which would mean that they are currently hearing about a lot of breakage at this time from their customers, easy enough to find out or at least eliminate through use of pins from another source, or it is specifically your problem, induced by an oddity on either the inner clamping surface of the nut or the clamped surface of the extension that is causing them to attempt to lock as one rather then slide under the load of tightening the two together.

I would through clean, with solvent, both the extension's face and the nut's inner flange and inspect them with magnification for signs of concentrated loading such as burnished or galled edges, high spots or machine tool chatter or merely the appearance of machining marks that may attempt to lock these parts with each other while torque is being applied.

Also examine the walls of the slot in the upper receiver, look for signs of high contact with the pin that may load it at its uppermost height instead of close to it's base at the extension, that coupled with greater than usual friction between the mating surfacing theoretically could provide the leverage to cause breakage.

Perhaps the receiver has a depression made by a shorter protruding pin from an earlier barrel and the new arrangement has the pin sticking out higher and only the very end is being loaded.

Also, if you use a reaction rod the torque load is directly applied to the extension between the nut and the reaction rod unlike when holding the receiver where the torque input at the nut is countered by the receiver's slot which can become a shear should movement between the two face of the nut and the extension lock up for some reason.

By holding the extension directly, an unusual amount of sliding resistance should be overcome easily by the torque directly countered between nut and extension without imparting any extra urge to rotate on the receiver's part.


Have you checked your torque wrench against another and are you greasing the mating surface of the nut and extension?

I've been to two different gunsmiths in town with the barrel and upper receiver in hand and both of them said they couldn't explain how that happened.  Unfortunately, both of them are running over a month behind with hunting season coming up and can't help me out right now.  So fucking frustrating to spend +$3,000 on a rifle that you can't get to shoot because of a $1.50 pin that keeps breaking.

Man, if you was in AZ instead of AR....I'd be over to get you set up in a hearbeat!!!  ( I have several friends that are machinists )



I want you to know that I KNOW YOUR PAIN, BROTHER!!!!!!!!!!!!!!!!!!!



You shall overcome, my Brother, you shall overcome!!!!!



If I can do it, you can!!!





 

Well what did you figure out?

You are starting off at 50lb.  I would torque to 30lb and then turn to index.

I've sheared an index pin off using a reaction rod.   My gut feeling is that a reaction rod puts all the torque on the index pin where as a clamshell or a No-MAR block somehow makes the
receiver and barrel nut take most of the torque.

I currently use a No-BAR block when torqueing a barrel on.  It's a little more aggravating to get the barrel nut and gas tube hole lined up because you are torqueing it on it's side but not that bad.

http://www.ebay.com/itm/NO-M-A-R-AR-10-308-762-Pin-Upper-Receiver-Vise-Block-Gunsmith-Barrel-Nut-Tool-/121768945140?hash=item1c59fea5f4

I do still use a reaction rod sometimes when putting on a flash suppressor.  

A lot of the problem with over torqueing a barrel nut trying to line up the gas tube can be solved but just buying an SLR rail.

The barrel nut does not have to be indexed.  There's no notches around it.  It has 4 flats on the barrel nut.  Just use a crowfoot or the SLR wrench to torque the barrel nut exactly to the torque you want.  35-40lb should be plenty.

When using an old style barrel nut that has to be indexed for the gas tube, I torque to 30 lb then torque over to the next notch in the barrel nut that lines up.

Instead of putting a ton of torque on the nut to get their, I bring it over some, break it loose, bring back a little more, and keep working it like that until I get it indexed.  Do this and you won't need to use as much torque to get it indexed.

Another aggravation is when you do to put on the flash suppressor.  308 crush washer can be a btch to crush.  You can end up torqueing too much and bend the index pin and shift the barrel.

Have found that a 3/4" ID piece of fuel line, cut about 4-5" long, and split down one side, slipped over the barrel will allow you to clamp the barrel in a vise tightly enough to usually crush the crush washer down to index the flash suppressor without
hurting the barrel.  

Just curious, is the barrel extension loose?  Can you twist it when the index pin is removed?  If it is, put some epoxy on it, tightening down snug, let it dry, then drop a new index pin in it and try it.  If the barrel extension is not tight it's going to twist and make it that much more likely to
shear off the index pin.

You can replace the index pin yourself.  They just drop in.  Use a magnet to get the broken part out if it doesn't just fall out.  You can get one here for $1.50

http://www.jsesurplus.com/ar15barrelextensionpinpinonly.aspx

I use plastic blocks(made from a cutting board from the dollar store) that fit between receiver lugs and clamp the upper receiver into the vise sideways, I install the nut torqued to 20, 30 and then 40ft lbs steps, then I simply use a dremel to clearance the barrel nut tit's to clear the gas tube. Absolutely no reason to over torque the nut.

I think i would send my upper to rainier for inspection and let them do attempt #3

Hope it all works out

I hope it's a mistake on your part but you are saying foot pounds, I'm sure it should be inch pounds.....

Foot pounds way too much.....

Doc

Ummm no. The barrel nut is always torqued in ft/lbs.

My Teppo Jutsu 458 SOCOM barrel's index pin folded when I used the Geissele Action Rod.

I had removed it from the DPMS LoPro receiver




and was mating it to my VLTOR MUR-1A upper receiver that was modified by Paladin Machine Shop
to open up the ejection port.





I went to the ARFCOM Geissele Forum and stated what had happened.  Geissele replied that it must
have been a faulty index pin and they would take care of it if I shipped it to them.  Well, hell, I had it back
in half a heart beat and put the Precision Instruments Split Beam to it one more time.



Thanks, Geissele.  BTW, the 458S has a SSA in the lower.  

Be sure and grease / lube the front side of the receiver extension flange and the receiver threads before sliding on the barrel nut.  This way less rotational motion from the barrel nut is transferred to the barrel itself.  Same principal applies whether you are using a receiver block or a reaction rod.

Sent upper, barrel, barrel nut, and bolt to Rainier (two day air at an expense of close to 50 dollars for me becuase I wanted it back as soon as possible) for them to install and headspace. Got it back three weeks later and this is what the extension looks like from inside the upper receiver:



Bolt installed in carrier and installed in the upper won't even begin to go into the extension because the barrel is turned in relation to the receiver. Gas port is not lined up so that confirms that the barrel and extension are turned. So it's not just me. Either the Aero upper has issues (don't now how...when everything is hand tight it lines up and bolt cycles in and out just fine) or there is an alignment pin issue. Either way, I sent it to Rainier for a solution and this is what I got back from them. Mac and Mike at Rainier have been helpful, but communication has been horrible...I've made at least three phone calls to Rainier and left messages with live people and never got a returned phone call.  Per request from Mike, I'm giving them one more chance to fix it. I'm rather pissed because a rifle that should have been done in July and available for a shoot this weekend is still fucked. Now I'm probably not even going to have it available to deer hunt with this year.

No. I've installed many barrels in the military with the TO open and the spec calls for 30-80 FT lbs.  In fact, I've had to tourque the ever loving fuck out of numerous barrels to get everything to line up and have NEVER seen a broken alignment pin. Another guy that just transferred to our unit said he did ~200 barrels a year at his old training unit and never saw a broken alignment pin...his experience mirrors mine with having to tourque the fuck out of many barrel nuts to get everything lined up.

I would be livid!! That looks like shit, hopefully they fix it.

I

That's not gonna work.  Would be surprised if the bolt would even lock up.  I've got a feeling that that barrel us not right.  I had a dpms barrel I bought used off gunbroker that I finally just threw in the trash that I had broke two index pins off on, the barrel extension had play in it and would turn a 1/4 turn more with the index pin out.  Got another barrel and no problem.

I'm not a gunsmith but as I understand it when the barrel extension is put on the barrel, the extension has to be cut back so that when the barrel extension is screwed on it bottoms out exactly lined up so that gas port is lined up perfectly and at that point that drill the hole for the index pin so that it will be perfectly lined up when it's pushed into the reciever.  If the barrel is cut back a little too much and you "fix" it by backing the extension off a little then drill and set the index pin now when you use a reaction rod the torque is not transferred from the barrel extension to the barrel, it all falls on the index pin, and will shear it off every time.

I would think the extension needs to be removed and a new extension put on and then cut to bottom out in line so that everything lined up.  Here's a post I found on another thread by someone that sounds like they know what they are talking about explaining why you can't fix the barrel extension if it's not cut right.

The extension is mounted during manufacture of the barrel BEFORE the chamber is finish reamed, BEFORE the index pin hole is drilled and pin pressed in, BEFORE the gas port is drilled, and BEFORE the front sight base is drilled and pinned.

OK, say you do. You screw on a new extension and torque it up. Oops! The extension is 27.8 degrees off. To the left. OK, you'll have to machine some off the barrel, enough so the extension will rotate around 360* - 27.8* = 332.2*. So, then you take the thread pitch, and machine off 27.8*/332.2* x thread pitch... well, I forget the thread pitch, but that's what you have to do.

Oops, now the handguard won't fit.

Chamber is too short. So you have to ream the chamber. Ooops, just ground the chrome plating out of the chamer.

Problems, problems, problems.

Anyway, with all you spend on the extension, the extension tool, and machinist's time, you might as well toss your USED barrel in the scrap iron bin and BUY a new barrel that already has a barrel extension, as it should be. It will be cheaper.

That's really screwed up.   How did they check the headspace on that before they sent it out?

The bolt will drop into the extension when not installed in the carrier. When in the carrier and put into the upper, the bolt won't line up with the bolt lug cuts in the extension. Won't even enter the extension.  The first and the second time I got the barrel, I put the barrel on and hand tightened the barrel nut and put the BCG in to make sure everything would work.  Bolt, charging handle, JP Silent capture buffer system, and trigger all functioned as designed.

It's packaged up again for try number three. I'm sending the barrel, barrel nut, complete BCG, gas tube, SLR Sentry 7 gas block, and A2 .30 cal flash suppressor with crush washer to them. If they can't send me a working upper back, I have absolutely no idea what I'm going to do.

Don't ask me how I know, but having an armorer's wrench mounted in a vise and using a "reaction rod" type tool can allow the barrel to "hang" down and allow the index pin to fall out of the slot, rotate, and cause the exact condition you have. I'll bet if you pull the barrel you will see a nice little mark on the upper receiver where the index pin got pinched between the upper and barrel nut.

Another note: the way the barrel extension is recessed in the upper is what makes me think the index pin is not seated in the alignment notch. I'd guess the depth of recess is the same dimension as the diameter of the index pin.

If it were me I would pull the barrel and fix it myself. I also would start at 30 ft/lbs (torqued three times using Aersoshell 33) and then increase torque until the gas tube lines up. I would set my torque wrench to 50 ft/lbs to try to get it to line up, since you know you can go to 50 ft/lbs without breaking anything.

You know what else I would do? I would start wondering if my torque wrench was in spec.

Not only check your torque wrench but also what wrench are you using on the barrel nut.

Be aware that if the 1/2" drive hole in your wrench is not in the correct spot you could be multiplying the torque applied. The moment arm is critical in applying the correct torque.

I didn't use a reaction rod the two times I installed the barrel and the alignment pin broke. I used upper blocks in a vice.  I hand tightened everything, torqued to 30 ft lbs, backed it off, and repeated three times before going for final tourque and gas tube alignment. I used two different tourque wrenches, one of which is on a 3 month calibration schedule so I know it is checked often.

This last time that Rainier installed and headspaced the barrel, I couldn't tell you what their processes are. I can tell you the result was the same as what I got the two times the alignment pin broke.

Barrel nut wrench is the one supplied by Midwest Industries with their rail and looks exactly as it should. MI also notes that 60 ft lbs is the max tourque value for their barrel nut and I was being very careful not to exceed that.

Video the bolt carrier not allowing the bolt to lock. Post it on youtube, call Ranier to have them look at it and these pictures. Ask them for a solution, and then video disassemble and post the sheared pin. Post that.

Is the barrel extention flush on the front of the receiver? Is there much slop with the extebtion just pushed in, no nut? Only question I haven't seen asked I can think of. The lapping tools for the reciers on an AR-15, II've seensome of those off quite a bit. All the friction on the nut surface, just a small area on the front of the receiver a possibility?

It's already on the way back to Rainier. To their credit, Mac and Mike have really been trying to help.  Their communication sucks, but when I finally do get in contact with them, they seem to genuinely want to make this right.

I have great respect for Rainier barrels, but I do believe there has been a thread or 2 now regarding index pins shearing.
Your installed barrel looks terrible.
I don't really understand how they couldn't see that.

By the way - you never answered my question about the barrel nut.

Which question is that?