Over torqued barrel nut

[BigK]

I loaned a co-worker my receiver blocks and AR tool to install his new handguard. When he hit 30 ft-lbs the top gas tube hole was just a mm post top dead center, so he tried for the next hole. At 60 ft-lbs he was still half way away from the next hole.

He realized he'd need to order some shims, so he tried to unscrew it. This is what happened:


We estimate that unscrewing the nut probably out about 80-85 ft-lbs of torque on the holes. Needless to say, a valuable leason was learned.

[R_Bert]

Perhaps also he wants to square the face of the upper?

 

http://www.midwayusa.com/product/821295/wheeler-engineering-delta-series-upper-receiver-lapping-tool-ar-15

[Luke E.]

 Well I guess He needs to order a new barrel nut with the shims huh ;) I would suggest receiver lapping tool that R_bert linked above rather than shims. Very little material will need to be removed to allow it to line up at 30ft.lbs. and sometimes just removing the finish is enough but if he's a whole hole off then he'll have to take just a bit more off. They aren't expensive and Outpost stocks them for I think $28.

[mikegideon]

I have the lapping tool. I didn't buy it to line up barrel nuts, but it will do the job

[BigK]

I didn't even think of suggesting lapping. He already ordered the shims before he told me.

[Clod Stomper]

Yup, the lapping tool.

 

Also, anti-seize grease (or another high-quality grease) on the threads.  Plus another trick that gunsmiths use to seat threads:  After applying the grease, tighten, then loosen, then tighten, then loosen, then tighten one more time.  You'll be surprised how much further the nut (or barrel, or whatever) will go.

[Rightwinger]

Yep, always stretch the threads a bit.

[Luke E.]

Not only will the lapping tool allow you to get your gas tube lined up within the correct torque range but it's main purpose, imo, is to ensure that the face of the receiver is true with the bearing surfaces that the bcg rides on which means that your barrel and extension will be properly aligned with the bolt. Even if he's ordered the shims already, personally, I would go ahead and buy or borrow a lapping tool and do it right. I'd be glad to loan mine to you so you can lap his receiver for him if the money is a concern. I haven't even used mine yet so you'd get to break it in ;) Just let me know if he wants to go that route and we can figure out a time to meet up.

[Dolomite_supafly]

He should have used grease and worked up in steps. Go part of the way to spec then loosen, then go a bit farther and loosen and continue until things line up. I suspect the biggest problem is tightening an anodized dry part onto another dry anodized part.

[Luke E.]

He should have used grease and worked up in steps. Go part of the way to spec then loosen, then go a bit farther and loosen and continue until things line up. I suspect the biggest problem is tightening an anodized dry part onto another dry anodized part.

 

 Tightening in a sequence like Dolomite is describing will not only get you around a little further but will also "pre" stretch the threads which will minimize any stretching later on causing the barrel nut torque to reduce with use. I seriously doubt if it would gain you a full hole worth of turn but every one is a little different. Definitely have him use grease when he reassembles.

[Dolomite_supafly]

Also, it looks like that is part of the cheap kits being sold on eBay. Nothing wrong with them as long as you follow the procedures for installing a tube but if you don't they will fail sooner than a quality piece.

[Luke E.]

Also, it looks like that is part of the cheap kits being sold on eBay. Nothing wrong with them as long as you follow the procedures for installing a tube but if you don't they will fail sooner than a quality piece.

 

 I wondered about what manufacturer the nut came from. I've also noticed some handguards will come with a little cheap stamped steel "wrench" that you stick a ratchet in and they seem to chew themselves and the barrel nut up pretty bad. There's also no shortage of cheap chinese AR "do-it-all" tools and they don't seem to mesh with the different barrel nuts very well. They seem like they fit pretty snug at first but as soon as you put a little force to them and the paint or whatever coating they have on them comes off all you're left with is a very sloppy wrench just itching to ruin a barrel nut. 

[Rightwinger]

Here's the grease to use on the barrel extension and threads.  Aeroshell

http://www.ebay.com/itm/AeroShell-Grease-33MS-Mil-spec-Moly-Barrel-Nut-Grease-Jar-5-ml-5-56-223-AR-/190852451462?hash=item2c6fb14c86&vxp=mtr

 

You get the little container in front of the commercial tube.  Little dabs will do ya.

[BigK]

Also, it looks like that is part of the cheap kits being sold on eBay. Nothing wrong with them as long as you follow the procedures for installing a tube but if you don't they will fail sooner than a quality piece.

Good eye. I'm pretty sure he got his rail from eBay and the nut came with it.

[Dolomite_supafly]

Lucky for him they sell replacement nuts on there, I guess it is such a big problem that there is a need to sell them.

[BigK]

I just found out today that he's having big problems manually extracting a round from his rifle. It's stuck so tight that I had to "pogo" it real hard to get the round to extract. This seems like way to much force for it to be as simple as a short throat and bullet engaging rifling. Without a round in the chamber, it still cycles kind of stiff and not very smoothly. It's real stiff at first 1/3 of the way back, then catches about 1/3 way back slightly, then gets noticeably easier after that.

Do you think it's possible that he torqued the receiver when he applied so much force to remove that barrel nut? He did use receiver blocks, but is it possible he clamped it so tightly in the vise that he partially collapsed the receiver in?

[Luke E.]

I just found out today that he's having big problems manually extracting a round from his rifle. It's stuck so tight that I had to "pogo" it real hard to get the round to extract. This seems like way to much force for it to be as simple as a short throat and bullet engaging rifling. Without a round in the chamber, it still cycles kind of stiff and not very smoothly. It's real stiff at first 1/3 of the way back, then catches about 1/3 way back slightly, then gets noticeably easier after that.

Do you think it's possible that he torqued the receiver when he applied so much force to remove that barrel nut? He did use receiver blocks, but is it possible he clamped it so tightly in the vise that he partially collapsed the receiver in?

Did he use one of the "clamshell" type upper vise blocks? I'm going to assume that he did because that's the most common type.
I doubt that he squished the upper receiver in the clamshell by over tightening the vise but it is very possible to twist/torque the receiver by using a cheap clamshell vice block and putting to much force on it with the wrench. A twisted receiver could definitely cause it to be hard to move the bolt carrier back and forth within the receiver. I would tend to think that it woul be really hard to twist one enough that it would require him to "pogo stick" it as you described. How much difference is there In required force when chambering and un chambering a round vs. just running the bolt carrier group back and forth with no ammo?

[Dolomite_supafly]

Yeah, he probably twisted the upper receiver and it will likely need to be replaced. I have seen a lot of people try to untwist their receivers and it rarely untwists where it is twisted.

 

Can you drop a live round in the chamber, push on it with your finger then flip it up and the round fall out? If so the barrel is likely not the problem and the twisted receiver is the problem.

 

Not sure how far away you are from me but if you want I can get this put together correctly. If the upper receiver is bent I cannot do anything to fix that but I can prevent it from happening again.

[BigK]

Thanks for the input Luke E. I had similar thoughts about the vise blocks (yes clamshell). They're el cheapos from Amazon, but he'd have had to really crank hard on that vise and likely cracked the blocks to squish his receiver. I just didn't wanna rule out any possibility just yet.

Can you drop a live round in the chamber, push on it with your finger then flip it up and the round fall out? If so the barrel is likely not the problem and the twisted receiver is the problem.

I had him try a round in in the barrel and verified it yesterday myself. The rounds drop free and are clearly shouldering far enough in.

My only reservation about the receiver being twisted was that it's so much harder to extract a live round than it is to charge the rifle on an empty chamber. It seems the cam pin would hang up whether there's a round in the chamber or not...same with the lugs on the bolt. My only guess is the part of the extractor that runs down the side of the bolt and acts like a leaf spring is what's hanging on something when a round is chamber due to the fact that it'd be just slightly spring outward.

Does that sound possible? If not, any suggestion on what part of the charging system would cause this kind of lockup with a round in the extractor vs no round? Edited October 17, 2014 by BigK

[Dolomite_supafly]

The whole upper receiver is probably all out of whack now. It is not the barrel if the round drops free.

 

The extractor will not spring out far enough to be higher than the other lugs. But with the receiver bent the round could be ever so slightly sideways in the chamber causing it to bind.

 

Those plastic blocks will bend and move out of shape with enough force and based on the barrel nut he went way beyond that.

[Dolomite_supafly]

Can we get a picture of the upper receiver from the bottom? With and without the bolt in it.

[Luke E.]

^ this. There is nothing that protrudes enough for anything BCGS related to hang up. That is unless the receiver is twisted. You can prove this to yourself by taking a BCG out of your rifle and trying it in his receiver. if the problem is still there (I think it will be) then you know the receiver is the problem.

[Dustbuster]

fwiw, i use "never seize" on critical thread apps it wont wick when heated up

[tnguy]

The whole upper receiver is probably all out of whack now. It is not the barrel if the round drops free.

 

The extractor will not spring out far enough to be higher than the other lugs. But with the receiver bent the round could be ever so slightly sideways in the chamber causing it to bind.

 

Those plastic blocks will bend and move out of shape with enough force and based on the barrel nut he went way beyond that.

 

You have to watch the fit too. The clamshell I got fit neither of the uppers I used it on and I had to carefully carve it down with a chisel to get a snug fit. I think if I would have used it as-is, I would have definitely had problems.

[Luke E.]

You have to watch the fit too. The clamshell I got fit neither of the uppers I used it on and I had to carefully carve it down with a chisel to get a snug fit. I think if I would have used it as-is, I would have definitely had problems.

 

 Were they billet receivers that didn't fit? Every clamshell vise block that I've seen has been made to fit mil-spec forged uppers and I've never seen one that would mesh with a billet receiver without some Dremel work