I was indexing the barrel on my M4gery flat top RR upper when I accidentally cracked the upper where the delta ring threads are. The crack is approximately 1/2 inch long hair-line crack that runs from the barrel pin index slot across the barrel nut threads. The front sight was not lining up correctly so I did like I read on ARF.com and, with the upper in a proper AR plastic clamp and in a vise, I tapped the front sight/gas block with a rubber mallet and cracked the upper where the barrel index pin goes into the upper. I went ahead and lined up the barrel anyway and then torqued the barrel nut to 80 lbs (measured exactly) with no problem. I then backed the barrel nut off just far enough to line it up with the gas tube, delta spring and delta ring, installed the gas tube and re-pinned the gas tube at the gas block/front sight. It appears that the crack stayed in the threaded end of the upper and the barrel nut covers almost all of the hairline crack. The threads are still straight and the barrel nut is threaded and properly torqued.

A> Do you think that this will be alright as it is with the barrel nut covering the crack and the crack supported by the barrel chamber?

B> Should I scrap the upper and start over with a new upper?

C> Can a hairline grack in the upper be repaired? The crack crosses the barrel nut threads.

Poll coming.

Sounds like an $80 learning experience to me... I wouldn't toy with it in that condition...

YMMV


- BG

I'd lose the receiver with a half inch crack in it and get a new one.

You now have an unsafe paperweight.
Chalk it up to "don't follow every instruction you read on the internet" and get another upper
While it is possible to tap the front sight into place it sounds like you whacked it pretty hard to the side and applied too much stress to the area of the barrel index notch. You should have loosened the barrel nut straightened up the barrel apply some grease to the barrel flange and retorque the nut I have been putting together uppers for a while and never had to use an impact adjustment tool to align the front sight.

time for duct tape.

Quoted: You now have an unsafe paperweight.

Perfectly safe as a paperweight I would think!

do not use it

Hell just get some JB WELD and let it harden and then sand it down and you will be okay. Really I would just get a new upper and be done with it.

Also, you are incorrect on your barrel torqueing procedure. Torque the barrel nut 31-35 ft-lbs, then tighten it till the gas tube lines up, applying no more than 80 ft-lbs torque MAXIMUM, the tube hole should line up long before you get to 80 ft-lbs.

U.S. Marine Corps Technical Manual TM 05538C-23&P/2 , Page 3-34 clearly states the following:
"The Barrel nut may be tightened beyond 35 ft-lbs to aline the barrel nut serrations for proper gas tube clearance. Never loosen the barrel nut to aline for gas tube clearance."

And Appendix F, Torque Limits for barrel nut: 31 ft-lbs minimum, DO NOT EXCEED 80 ft-lbs to aline slot

 Put it in here.  


 

Colt_SBR

You should give yourself a vasectomy before you pass your genetic code down the line, Babe!

Like I always say....  Take it to an Armorer!

Quoted: You should give yourself a vasectomy before you pass your genetic code down the line, Babe! Like I always say....  Take it to an Armorer!

Come on... you know that post is a joke.

Quoted: Come on... you know that post is a joke.

You're right!  NO ONE is that damned dumb!

let your brother in law borrow it, then ( provided it doesn't blow up in his face)  accuse him of breaking it when he returns it, but if you don't have a suitable in law to blame it on, scrap it and buy a new one.

Nothing like using "almost" all the needed tools to install the barrel.

Wait, if memory serves correctly, you don't need to use a torque wrench to install the barrel!!!

Quoted: I was indexing the barrel on my M4gery flat top RR upper when I accidentally cracked the upper where the delta ring threads are.

"Delta ring threads"?

The crack is approximately 1/2 inch long hair-line crack that runs from the barrel pin index slot across the barrel nut threads.

Okay,

The front sight was not lining up correctly so I did like I read on ARF.com

Hmm, that's where you began to go wrong.

and, with the upper in a proper AR plastic clamp and in a vise, I tapped the front sight/gas block with a rubber mallet and cracked the upper where the barrel index pin goes into the upper.

That is a very good way to crack your upper receiver!  The pin is steel, and it's in a steel barrel, and you whacked it with a mallet.  Did you imagine that the nice thin aluminum with the nice threads would be happy with that?  Next time file the notch in the direction you want to go and shim the off-side with a little piece of soda can.

I went ahead and lined up the barrel anyway and then torqued the barrel nut to 80 lbs (measured exactly) with no problem.

Pretty dumb.  You trashed the upper and then went ahead and assembled it?  Why?  And next time throw away the torque wrench.

I then backed the barrel nut off just far enough to line it up with the gas tube,

Back-asswards.  Tighten 'til snug, then a little more until the next gap lines up with the hole.

delta spring and delta ring, installed the gas tube and re-pinned the gas tube at the gas block/front sight.

Again, a lot of wasted work on a busted upper.

It appears that the crack stayed in the threaded end of the upper and the barrel nut covers almost all of the hairline crack. The threads are still straight and the barrel nut is threaded and properly torqued.

And all the stress of firing is focused on that nice cracked upper.  How long do you think it will last before the barrel falls off?

A> Do you think that this will be alright as it is with the barrel nut covering the crack and the crack supported by the barrel chamber?

NOPE.

B> Should I scrap the upper and start over with a new upper?

YUP.

C> Can a hairline grack in the upper be repaired? The crack crosses the barrel nut threads.

Trash it.

Quoted: I was indexing the barrel on my M4gery flat top RR upper when I accidentally cracked the upper where the delta ring threads are. The crack is approximately 1/2 inch long hair-line crack that runs from the barrel pin index slot across the barrel nut threads. The front sight was not lining up correctly so I did like I read on ARF.com and, with the upper in a proper AR plastic clamp and in a vise, I tapped the front sight/gas block with a rubber mallet and cracked the upper where the barrel index pin goes into the upper. I went ahead and lined up the barrel anyway and then torqued the barrel nut to 80 lbs (measured exactly) with no problem. I then backed the barrel nut off just far enough to line it up with the gas tube, delta spring and delta ring, installed the gas tube and re-pinned the gas tube at the gas block/front sight. It appears that the crack stayed in the threaded end of the upper and the barrel nut covers almost all of the hairline crack. The threads are still straight and the barrel nut is threaded and properly torqued. A> Do you think that this will be alright as it is with the barrel nut covering the crack and the crack supported by the barrel chamber? B> Should I scrap the upper and start over with a new upper? C> Can a hairline grack in the upper be repaired? The crack crosses the barrel nut threads. Poll coming.

Ok, I don't see how you are going to get the front sight to align by hitting it with a hammer.  I know that we hear of these Bushmasters with over torqued barrel nuts that the front sights lean over on because the barrel index pin is starting to shear, but it takes quite a bit more than 80ft-lbs to do it though.   If you put the barrel in correctly, any misaligned front sight towers are going to be because there was a screw up when they made the barrel.

Someone posted that the Marine armorer's book says never to back it off to align for the gas tube.  While I agree with this, and I will tell in a minute, I don't think this caused him to crack the upper.  I only align from the clockwise side.  I am not sure if it matters, but I feel that it makes the threads grip better.  I take the barrel nut to pretty stiff torque and then back it completely off.  This makes the threads mate.  I can't help but think that having the most contact with the threads would be a good thing, even it it doesn't matter.  A very real reason is that it makes the the final alignment so much smoother.

I don't think that is unsafe.  I mean, come on, the upper doesn't have hardly any stress on it because of the design of having everything lock to the barrel extension.  The force of the barrel nut will push the threads of the upper down onto the barrel extension.  You say that the barrel nut almost covers the crack.  I think that the crack could extend if you hit the barrel hard enough, although I wouldn't want to be there when you did it.  I would imagine that it would take quite a blow.  So, while it might not be unsafe, I would imagine that it might have a wandering zero, and could create future problems down the road.


But since you already have it put together, why not see what happens?  I mean, if it bothers you, use a string to pull the trigger.  Test to destruction is the only type of test I like to participate in!

Carbine_Man, it seems that you seem to have a pretty condecending attitude towards the thread starter.  Come on, it wasn't like you paid him to put together your upper?  WTF, he was just stating that he messed up, and asked for advice on what the proper course of action was now.  I am sure that he didn't spend his time posting just to have someone tell him he was a fucking idiot.  Pretty trollish behavior.



Just get a new upper and put the old one on the shelf above your upper block and barrel wrench to remind you not to hit the front sight base with a hammer.

80 foot pounds is absolute max. I'm happier at about 40 foot pounds.

Scrap it. I would pay $80 to know that it wasn't going to break on me. Hell, I'd pay more than that, but you get the point.

Quoted: Carbine_Man, it seems that you seem to have a pretty condecending attitude towards the thread starter.  Come on, it wasn't like you paid him to put together your upper?  WTF, he was just stating that he messed up, and asked for advice on what the proper course of action was now.  I am sure that he didn't spend his time posting just to have someone tell him he was a fucking idiot.  Pretty trollish behavior.

YOU ARE ABSOLUTLEY RIGHT!!!  But it sure felt good to write!  

I cracked an old SP-1 upper trying to get the 30+ year old barrel off.

I ended up using it with an 1:12 twist M16A1 barrel and a Ceiner 22LR conversion.

I won't fire 5.56mm out of it, but I think it's OK for plinking with .22 Long Rifle.

If you need 5.56mm, go buy another upper receiver.

W.E.C.S.O.G.!

Its a paperweight now. Im with Markm on this- take your stuff to an armorer.

Quoted: I don't think that is unsafe.  I mean, come on, the upper doesn't have hardly any stress on it because of the design of having everything lock to the barrel extension.

Seeing as how the barrel is attached to the upper, all recoil forces are transmitted to the upper receiver before the bolt unlocks.  You might eventually end up with a two-piece upper.

Can you please post a photo of your cracked upper?

Pale pony,

Sorry to hear about your luck.  Thanks again, though for that great post ban RRA barrel!

Quoted: ..... I went ahead and lined up the barrel anyway and then torqued the barrel nut to 80 lbs (measured exactly) with no problem.

Who told you to go that high?  That is a MAX torque value and you really shouldn't be up that high in most cases.

I then backed the barrel nut off just far enough to line it up with the gas tube, delta spring and delta ring,

Ok I don't know why your think you are qualified to install a barrel.  Turn in your tools - buy a new upper and send it to someeone who DOES know what they are doing.

NEVER torqe a barrel then 'back off' to line it up for the gas tube.  By backing off you've loosened the nut and now it's free to loosen some more.  You are supposed to torque to 30 ft-lbs then torque higher to align for the gas tube - NEVER NEVER loosen to get the alignment.

I suggest you download a copy of the -23&P (Unit & Direct Support Maintenance Manual) and read the darn thing.  It has complete directions on installing a barrel.  It's a free download and be had if you click on the Information button above.

TOSS IT!!!!!

Send it to me...I wanna practice welding Alum...If you wanted it back it might look like an ash tray when I am done!

If the crack is visible behind (receiver side) of the barrel nut, it will continue to propagate.   Without seeing a pic, it sounds like a crack started at the stress riser caused by the milling of the slot into  the threaded area.  If so, this will "work" every time the bolt slams home.  

Will it function with the crack?  Probably.

Is it considered safe?  My vote is no.

On a similar note...I just got my new YHM HGs yesterday, and just HAD to get them on last night...actually after trying for a couple of hours it was a matter of principle...they were going on.

I had read that they're a little tough to get on, so I expected it.  They seemed to get close to going on, so a little rubber mallet action came into play.  Then the dremel.  Then the mallet again.  Well, now they're on, then got to thinking, hope I didn't screw up the upper!  The barrel nut was worse for wear, the delta ring was scratched up, but aluma black took care of that.   Started thinking about it more today and called Calvin at Brightflashlights.  H explained what the problem was, and that the receiver was probably okay.    If I had just called Calvin first, he had a simple fix, but noooooo! I had to do it.  So now it nags me me on whether or not I might have damaged the upper. The YHM HGs are great, and I have never dealt with a nicer person than Calvin.  But, I shouldn't own a hammer.

I reserve comment for the time being.