Just today, I found that my nice tight groups suddenly went hay-wire, so after inspecting the mounts, scope, etc. I discovered that the barrel and upper reciever had a bit of play between them. I tightened the barrel back to the upper, at which point the play was eliminated...hopefully this will solve the problem.

With this in mind I am now wondering....Just what keeps the barrel tight to the reciever?? It dosn't seem like the gas tube can keep the nut from turning, and I didn't see anything that is in place to keep the nut tight...am I missing something here??

I would appreciate your imput fellas since I am wondering if it will become loose again!

Thanks Frank

Don't take this as gospel, but believe it is something in the area of 35in/lbs.?? Someone here can give you the correct torque I am sure.
You mention that you tightened it back and that requires use of barrel wrench which mates with the "star" nut which threads into the upper reciever and pulls the barrel back into place.
There is a shoulder on the barrel extension(15/16 barrels are two pieces with the chamber end actually threaded into the barrel itself)and by torquing as described headspace is determined. Do you have headspace gauges?? If not, would suggest you find some/borrow/buy, etc. and you will have Go Gauge and No Gauge to determine headspace(most disregard the Field Gauge.) There is a lot more to it than I have said and you definitely do not want the two items, barrel and upper receiver installed incorrectly, that's a NO, NO. Should mention that when using the gauges, remove ejector pin and extractor to determine correct headspace. If you are going to do this work yourself, find a manual/book which will give you all the specs required to build a safe and functioning firearm. You can do a search for building a 15 and glean a lot of info from that.
Hope that someone on here gives you correct torque settings and steps you should take to correct your problem.

Thanks MFD,

No I didn't torque it, but I do have the barrel wrench and I tightened it as much as I could...I then had to back it off a bit in order to line the gas tube up with a slot.

It is damm tight

OK, I did not mention earlier, but if worst case senario you do not have gauges, when inserting bolt/carrier, note if the bolt carrier is flush, dead even with the rear surface of the upper reciever when closed all the way forward, in battery if you will. If it is a very smooth obvious flush surface there, you probably have good headspace, but probably is not the way to go, check it with gauges for safety and function sake.

On an AR 15 you first put moly grease on the threads and also the face of the barrel extension flange. The grease is applied to stop corrosion as the nut can corrode and weld itself to the upper receiver threads. I put grease on the barrel extension flange because the nut can grab it when it's dry and try to rotate the barrel if you don't have the barrel clamped and this will divet the rather thins area of the threads where the indexing pins is. The proper way to torque is to have the receiver in a receiver block clamped in a large enough vice. Then I clamp the barrel so it won't turn. The armor books say torque to 35 foot pounds three time. That torque, back the nut off, then repeat this again, then final torque the third time. This is to set the threads. You will more then likely find the gas tube hole in the barrel nut isn't lined up with the hole for it in the receiver. You then torque higher until the next hole lines up. You NEVER loosen the barrel nut to align the gas tube holes. So you can have a torque anywhere from 35 foot pounds and up. They can get pretty high. I won't give a figure so as you won't attempt to go that high. Just go until the next hole lines up.

I'm afraid you may have ruined your receiver. This depends on how tight is according to you. So loosen it and then torque to where the gas tube holes line up. Let's say for example you have it torqued to 48 foot pounds. You don't want to loosen it and then torque to say 38 foot pounds to align the holes. You actually need to find out what the barrel nut is torqued to now so you can set your torque wrench to that figure or a little bit above it to where the gas tube holes align.

SmokinJ,
I did put the upper in a vice, and when it stopped tightening the holes were not lined up.
As I said before, I didn't use a torque wrench, but I couldn't even budge it any tighter to line the holes up, so I had to back it off a hair to line them up.

I really do regret it now that I tried to do this myself, but with that said, what do you think I should do??

It is damm tight, but do you feel that it will loosen up again or something even worse??

Point me in the right direction please

quote:

Originally posted by Leopardtrack:
SmokinJ,
I did put the upper in a vice, and when it stopped tightening the holes were not lined up.
As I said before, I didn't use a torque wrench, but I couldn't even budge it any tighter to line the holes up, so I had to back it off a hair to line them up.

I really do regret it now that I tried to do this myself, but with that said, what do you think I should do??

It is damm tight, but do you feel that it will loosen up again or something even worse??

Point me in the right direction please

Does it head space and are the sights and gas tube in line now if so shoot and see what happens. If it loosens then you well have to try something else.

If it losesens then dismount it get a new barrel nut AND A TORGUE WRENCH and try again.

Then if it dosen't hold or properly mount there is a good chance you streached the threads on your upper.

Then you buy a new upper get some help in mounting the barrel. Write the fist try off as a lessen will learned.

I had told you what I would do. P Dog had some good advice too. You could try it.

A torque wrench is long and has lots of leverage, it has to to give torque rating as high as 150 foot pounds. You probably used a shorter regular wrench right?

Most the barrel nuts that I have dealt with come lose right away. In other words they are not tight for a long time turning them off.

Also putting grease on them makes a difference too besides keeping them from corroding together. If you have an aluminum barrel nut that is aluminum against aluminum and that is pretty grabby, especially when both the nut and threads are anodized.

If you feel it's very tight you may try shooting it and see what happens. I'll tell you this though, if you use it for years and then decide to take it apart for whatever reason it may corrode together and will be very hard to take apart. More then likely it will not though.

Head spacing has to do with the bolt and the barrel extension. I don't see the tightening the barrel nut having much to do with that unless your barrel turned and the barrel extension lugs aren't lined up with the bolt lugs. You can tell this too if the gas port hole isn't lined up dead nuts at 12 o'clock, plus the front sight if you have the A2 type front sight and gas block. Also the feed ramps should be lined up to the feed ramps on the receiver.

Good luck in what you find.

Hey fellas,
Back to the range today and found that the tightening of the barrel did the trick with my groups going back to normal...if it stays that way remains to be seen!

SmokinJ...no more "gunsmithing" for me...I will leave that to someone who knows what they are doing next time something needs fixing.

I plan on shooting it for now and see what happens....if it does loosen up again I think that I will just go and buy another upper with a good lesson learned.

Thanks to all of you!

quote:

Originally posted by Leopardtrack:
Hey fellas,
Back to the range today and found that the tightening of the barrel did the trick with my groups going back to normal...if it stays that way remains to be seen!

SmokinJ...no more "gunsmithing" for me...I will leave that to someone who knows what they are doing next time something needs fixing.

I plan on shooting it for now and see what happens....if it does loosen up again I think that I will just go and buy another upper with a good lesson learned.

Thanks to all of you!

Well don't say no more gunsmithing, just learn how to do what you want to do first by asking someone skilled in the trade and by reading good books. Barreling an AR is pretty easy to do with the correct tools and knowledge which you have recently learned more then you started out with.

Hope it shoots fine for you and holds tight. If not you know how to assemble it correctly now.

aluminum upper to a steel barrel the aluminum will stretch and as you found out the barrel will become lose even with the gas tube in place. Between 35 and 55 pounds don’t loosen the barrel to get the gas tube to lineup I take an old gas tube and cut it to use as a locator pin torque the barrel to 35pounds then put the cut down gas tube in and start to increase the torque until the cut gas tube lines up with the barrel.

I believe a 3/16ths rod can be used to align the gas tube hole, or as mentioned you can use the gas tube. The fat part of the tube has to go through the holes. I don't know what the previous poster meant by using a small tube. The holes should also be lined up perfect because the tube should have a little flex to it and I'm talking about the part of it that is exposed inside the receiver.

I was talking about the gas tube that I cut down to about 4 inches when I said small tube sorry wasn’t clear . At my old job I would do around 200 barrels a year if you don’t tighten the barrel down the 3 times they will come loose .

quote:

Originally posted by MT:
I was talking about the gas tube that I cut down to about 4 inches when I said small tube sorry wasn’t clear . At my old job I would do around 200 barrels a year if you don’t tighten the barrel down the 3 times they will come loose .

No problem, my fault as I didn't understand what you were saying.

Yup you have to set those threads and torquing the three times does that. Some get away with just torquing once and think the three times is just BS. You've done enough barrels to know other wise.

I thought that torquing the barrel 3 times was BS also, but then I moved to a place that had 300 blank fire M4s and 900 live fire M4s we would replace at leased 150 of the blank fire barrels a year and around 50-75 of the live fire the blank guns would fell headspace at around 8000,10000 rounds. If we had a new guy that didn’t torque them down 3 times about 1out of 6 would come lose.