I'm installing a new 16" barrel on a flat top.  I've never put one on before.  I have everything I need.

How tight do I torque the barrel nut?  It is critical?  I assume I will need a torque wrench.  Is it the correct torque that usually produces the right headspace?

Thanks for any info anyone can give me.

I'm sure someone here will know, but I have called Bushamster for tech help in the past and they have put gunsmiths on the phone, all of whom seemed to really know their stuff.  They would be able to answer your question to a tee.

Just off the top of my head I think it's 30 ft/lbs but for goodness sake check that.

Tips I can pass along is torque and loosen three times. Use anit-sieze compound as spec'ed. And yes, you do need a torque wrench - even a cheap one.

Torque has nothing to do with headspace - unless you are attaching the barrel extention to the barrel - which would be really odd as most are sold together. Headspace is measures after assembly and is either pass or not.

Quoted: ...I have everything I need...

gee, I guess NOT!

Don't think about doing this for the FIRST time w/o the manual!!!!



Use the proper tools and manual:

Colt manual: CM102
USMC: TM 05538C-23&P/2

Paul's got it right. The only thing I would add is to not exceed 80ft-lbs on the final torque. In other words, if you can get everything to line up between 30 to 80ft-lbs, you're good to go.

Quoted: How tight do I torque the barrel nut?  It is critical?  I assume I will need a torque wrench.

The correct torque numbers are posted here:  www.ar15.com/forums/topic.html?b=3&f=7&t=98002

The danger of too much torque is that you will shear the indexing pin.  A torque wrench costs $20 to $50 from an auto parts store.

You obviosly DON'T have everything you needf as you obviosly haven't read the manual.  Go here: old.ar15.com/books and download the -23&P.  It has the complete instructions, tool list (yes you need a torque wrench and the barrel wrench - don't forget the Moly/Di-sulfide grease w/o graphite), and even pictures to help.

Thanks everybody for the advice.  I do have a torque wrench, barrel vice and barrel lug wrench.

I printed out the manual.  Thanks Forest for the link.  It has been a long time since I have visited the old AR-15.

It doesn't look too hard.  I'll give it a try this weekend.

Again, thanks.  

You need:

Barrel wrench aka armor's tool (DPMS TL-02 is fine).

Torque wrench with 1/2" drive (regular automotive type)

I suggest you NOT use barrel vise jaws (like DPMS #TL-05), as these will allow you to easily twist the barrel in the upper rx, and have a misaligned front sight.

Instead, I suggest you use an "action block", such as DPMS PR-02.  It is well worth the extra cost, even for doing only one barrel.  

Lubricate the threads with moly grease, yes, regular wheel bearing grease.  With the torque wrench engaged in the barrel wrench, torque to 25 ft-#, then back it off.  Tighten a second time to 30 ft-#, then back it off.

(The reason for this is to smooth the threads so that you get an accurate torque reading.)

Now, (you are going for the gold this time) torque it to 35 ft-# (your minimum).  Using a gas tube, or a piece of drill rod the same diameter as the gas tube, check that you can pass the rod or tube through the uppermost notch and into the hole in the receiver.  Probably it will not go.

Torque a little more, and try to get it so that it that the drill rod will pas through, and swing and equal distant both ways.  Do NOT back it off to get proper alignment.  You can torque up to as much as 50 ft-#'s.  It is MY recommendation to torque from 35-55 ft-#'s (the manual is a little lower and higher), and you should be able to obtain tube alignment within this range.

You can go as high as 65, but as you go higher than this, you run the risk of stripping threads, ruining the upper receiver.  The first notch that properly aligns the gas tube after you reach 35 ft-#'s is what you are trying to achieve.  Torquing higher does not make for a better barrel installation or a safer rifle.

But yes, get a manual.

Your second question... The torque of the barrel nut has nothing to do with headspace.  That is determined by the fit of the bolt inside the barrel extension.  I have never had a new bolt not headspace correctly in a new barrel, but it could happen.

(Let's see if I can get away with posting this without Brouhaha or Tatjana chewing on me... hah!)