AR-15 barrel wobble?


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Guy de Loimbard
November 7, 2006, 06:43 PM
I have had a High Standard AR-15 for a little over a year now. Last month I started practicing weekly with it. That means I get to clean it more. Tonight while I was cleaning it I noticed that the barrel wobbles. If I hold the upper reciever with one hand, and the barrel with the other hand, I can rotate the barrel a teeny tiny distance - maybe not even a full degree - counterclockwise and then back. The front sight block and handguard move with it. If you look up from the underneath, even the gas tube will move when the barrel is turned.

My question is, is this normal? The barrels on my other guns hold on to the receiver solid as a rock. Is something broken in my AR that I can't see from the outside?

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iamkris
November 7, 2006, 07:01 PM
Not normal...meethinks you have a loose barrel nut. Get thee to a gunsmith or buy a good quality multitool and tighten it youself.

I'm not sure if this condition is actually unsafe but it certainly isn't good for the moving parts that have to lock up with the barrel...especially the bolt lugs taht need to you through their mates on the barrel extension. I personally wouldn't shoot it in this condition but maybe someone with better knowledge can validate.

Beren
November 7, 2006, 07:02 PM
Might be that the barrel nut is coming loose. This happened on a 9mm AR I built, when I didn't torque the nut down properly. Handguards started to wiggle a little, and when I checked further I saw it was the barrel nut, not the handguards. I took the nut off, then torqued down properly.

If you're comfortable with tools and don't mind taking small risks, you can always take the nut off and re-torque. Not SURE that's your problem, mind you. Is there a local smith who might take a look?

wanderinwalker
November 7, 2006, 07:02 PM
Sounds like a loose barrel nut to me. Installed a new barrel on one upper and didn't get the nut down tight enough and got the exact same kind of thing you describe. Torqued it down another notch and bingo, problem solved.

It can be solved yourself, with a vice, a wrench and an action block. For the cost of the above, it may be worth returning to manufacturer, having a gunsmith do it or finding a shooting friend who has the tools.

High Standard makes AR-15s now?

DougW
November 7, 2006, 07:30 PM
The gas tube has to be removed before you can tighten the delta nut. Removing the front sight to get the tube out may be the easiest to do. Then, loosen, add some anti sieze paste, tighten, loosen, tighten, loosen, then torque to 50 ft/lbs (I think that is the ammount, check ar15.com to be sure). Then tighten further to align the serrations of the delta nut so that the tube will pass into the upper, but don't go past 80 ft/lbs. Reinstall the tube or front sight and head for the range. You may have affected your windage, so resighting will be necessary. (Ask me how I know about this.:banghead: )

Guy de Loimbard
November 8, 2006, 02:27 PM
Thanks guys. Hopefully I can get this done soon, but I'm not to sure since I would probably have to drive down to Marquette to have it fixed by a smith. May just send it in.

Along the same lines, I have had a couple of FTE's lately that I figured were caused by bad ammo. The spent case stuck in the barrel and had to be pounded out with a cleaning rod, because the extractor had ripped the rim off the case. One of them was missing its primer. I figured it was just weak material used to make the case. Could they instead have been caused by the bolt opening and recoiling early due to the barrel not being lined up properly?

In any case I don't think I'm taking it out shooting. I figure best case scenario is 40k PSI shearing off the rest of the barrel nut threads and sending the barrel downrange a few feet, most likely case scenario is it explodes on me :what:

Gary G23
November 8, 2006, 03:02 PM
It must have been loose when you got it. With the gas tube in place it can only back out so far.

DnPRK
November 8, 2006, 11:16 PM
Check out http://www.ar15barrels.com/data/barrel-nut-index.pdf
Randall can sell you indexing shims.

The proper torque is 35 ft-lbs but is done in 3 stages:

1st apply light grease to the receiver threads and torque to 15 ft-lbs, then back the nut off.

2nd torque to 25 ft-lbs, then back the nut off again.

Finally, torque to 35 ft-lbs or whatever it takes to line up the gas tube notch. Torque should not be excessive with the shims. An upper can break if over torqued. I have a buddy who lives by the philosophy "more is better" and he cracked his upper while torquing the barrel nut with a 24" breaker bar.

PvtPyle
November 8, 2006, 11:45 PM
No, it is not a loose barrel nut. The loose barrel nut is what revealed the problem. The problem is that the barrle lug at the 12 o'clock position is smaller than the notch it locks into on the receiver. This was a common problem on the E series barrels on the issued Colt M4's (and their lack of customer service on the guns is one of the big issues that helped cost them the military contract).

So even if you tighten it back up to specs, because there is play in the lock up, it will loosen back up and you will be back to square one again. The parts are most likely out of spec on both sides, but one part is for sure. You could have them gauged, but remember that if the upper is peened at all inside the notch, it is toast.

Can the upper and barrel, save what you can from it and buy another. Thats what we had to do for three entire line companies.

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