I've noticed that some people are saying to use 80ft-lbs, but the TM says to use 30ft-lbs when coupled with the barrel nut wrench.

Which is it?  Does the wrench mechanically increase the torque by that much?

Also, having never used a torque wrench before, how do I know when it reaches the correct setting?  Is it when I feel the slight "give"?

Throw away the torque wrench.  Tighten the nut till it's snug with the wrench then turn some more till the next notch lines up.  

Now let the flamefest begin!!!!!

This is a hotly debated topic around here.  The traditionalists use the torque specs.  Smarter people use the above method as was originally penned here by Homo_Erectus.  I'd tell you to search, but ya can't do that anymore.

The 35 ft, lbs. is what the Airforce manual calls for and Colt call for. Te ARMY manual calls for 80 ft. lbs., and I don't recomend it, 80 ft. lbs. is a lot of torque on 1/8" of alum. around the barrel extension! Go Airforce on this one, don't forget the Airforce were the driving force behind adoption of the M16 in the first place. The Army were also the ones telling troops the weapon was self cleaning of all things.
Jack

I'm definately not an expert on this, but I have done it a few times. so I'll tell you my mistakes so you don't make the same ones.

First, if your using a G.I. barrel wrench that has 3 pins that engage the barrel nut, I recomend buying one of the armorers wrenches that has teeth to engage the barrel nut almost all the way around.  The first time I installed a barrel I used the G.I. type wrench.  When trying to torque the nut enough to align it for the gas tube, the wrench turned a little and slipped off the nut, damaging a few of the teeth on the barrel nut (unfortunately one of the marred teeth was where the gas tube fits through and it caused the gas tube not to fit properly even after it was aligned) and chipping the delta ring.  I haven't had this problem at all with the larger armorers wrench.

Second, I usually torque the barrel nut to 35 lbs. with the torque wrench then remove the torque wrench to tighten the barrel nut enough to align it to the gas tube (you usually have to go beyond 35 lbs. unless your really lucky).  The reason I do this is because the wrench feels much less secure (although not nearly as unsecure as the GI type was) while using the torque wrench for leverage.  I think it has something to do with the torque wrench being off center with the barrel nut, unlike the handle of the actual armorers wrench.

Third, I recomend using a armorers action block, the barrel block clamp that I had was very hard to get tight enough to hold the barrel securely and I ended up with aluminum smears all over my barrel on my first attempt.  

That poor old bushmaster barrel I first assembled sure saw a rough time.  I ended up filing off the offending barrel nut tooth (there were still plenty left to engage the wrench) and replacing the delta ring.  I have been thinking about selling it in favor of a 16 inch M4 barrel, but I'm not sure what would be a fair price to ask with it's flaws, even thought they are all hidden once assembled.  It has one other hidden flaw under the muzzle break (I tried to dimple the barrel for the muzzle break set screws with a hand drill and didn't do a very pretty job, but this is also hidden), but I'm getting a little off topic now.  Anyway, hope this helps.

PS. - Anyone want me to assemble your upper reciever for you?  Just kidding!

Quoted: Throw away the torque wrench.  Tighten the nut till it's snug with the wrench then turn some more till the next notch lines up.   Now let the flamefest begin!!!!! This is a hotly debated topic around here.  The traditionalists use the torque specs.  Smarter people use the above method as was originally penned here by Homo_Erectus.  I'd tell you to search, but ya can't do that anymore.

What he said.

Doesn't the USMC manual say between 31 and 80 ft-lbs?

Quoted: The 35 ft, lbs. is what the Airforce manual calls for and Colt call for. Te ARMY manual calls for 80 ft. lbs.,

BZZZ! I don't think so - thanks for playing .

The US Army and the US Air Force use the EXACT same manual (Heck I wouldn't be surprised if the AF sent their armorers to the Army school for armorers - the USMC does).

The manual is Army TM9-1005-319-23&P and in the Air Force its called the TO 11W3-5-5-42 otherwise knows as Technical Manual Unit and Direct Support Maintenance (Including Repair Parts and Special Tool List).  Both numbers are plainly marked on the cover.

Now what tha manual says:
On page 3-41 it clearly says in step 9 "...torque barrel nut assembly (9) to 30 ft-lbs (40.5 N-m)...."

Then at the top of page 3-43 there is a Caution box which reads "Do not torque over 80 ft-lbs (108 N-m) while tightening the barrel nut assembly to the next hole..."

Both the Army and Air Force use the 30ft-lbs as a starting torque and warn against going over 80 ft-lbs when going to the next hole.

Quoted: Both the Army and Air Force use the 30ft-lbs as a starting torque and warn against going over 80 ft-lbs when going to the next hole.

Exactly. I have never figured out why anyone wouldn't follow these SIMPLE directions, but there are still some who "know better" than the military armorers.

Reread the military manuals, they do NOT state that you assemble it at any given torque figure.  They state a minimum, and caution about going over 80.

Anyone who has bent wrenches a few times can feel when something is tight enough, no slack, secure.  That is the 30 ft-lb minimum.  There is no magical torque figure where the notch will line up, and it is not possible to manufacture this design to do this.  You just don't want it too loose so that the barrel flops around in the receiver, or the nut to back off by itself.  And you don't want to go too tight and strip the threads.  Somewhere between 30 and 80 there should be a spot where the notch lines up for gas tube insertion, which must be done to assemble this rifle.  So, snug it up and go tighter to align the notch.  Simple.

In this day and age, I just can't understand installing barrels using the barrel vise jaws when we can easily get action blocks from a number of sources.  This is a no brainer.  Only use for barrel vise jaws is to keep from twisting the barrel in the receiver when installing or removing flash hiders.  But if you want a canted sight, go on and use barrel vise jaws for barrel installation.

Quoted: .... But if you want a canted sight, go on and use barrel vise jaws for barrel installation.

Interesting comment.  I know people who claim its the opposite, that the Bushy 'over torqued' barels (canted front sights) are due to the use of the action blocks.

Heck if I know - However, I use the action blocks and have not had a serious cant issue on my uppers.

I use an action block, and had one barrel that had a significant windage problem.  The indexing pin fit very loosely in the receiver, so the barrel would twist to the right when you tightened up the barrel.  Both the barrel and receiver (A2) were BFI.

I eventually just installed the barrel and then banged on the FSB with a mallet until it straightened out.  Not exactly my method of choice, but it shoots strait now.

BFI recievers in general seem to be looser than other brands I have used.

Quoted: I eventually just installed the barrel and then banged on the FSB with a mallet until it straightened out.  Not exactly my method of choice, but it shoots strait now.

From what Tweak says, that's an accepted (and common) method of repair.

BFI recievers in general seem to be looser than other brands I have used.

I've not seen that with my A1 & A2 uppers.  However for flattops I've been taken with the ones Fulton Armory sells.  I buy the numbered flattop and the Bushy barrels fit in them perfectly - zero slop that I can tell for the pin or the barrel.  It doesn't get any better.

Damn the Search function...


If it was working, the Homo_Erectus clause would have been excersized before this thread even came to be...

Here ya go..................

Copied from Homo_Erectus: The Famous Homo Erectus Barrel Mounting Method - You'll need an Action Block and a Barrel Wrench, and that's all the special tools you'll need. I'm assuming you already have a vise, hammer and punches, files, and circlip pliers. Forget the torque wrench and all those silly "tighten and loosen 17 times while waving a dead cat over the barrel nut and dancing naked in the moonlight chanting voodoo curses with your nutsack smeared with magic moly grease" procedures incessantly parroted my the Worshipers of Military Manuals who until recently confined their insanity to the Troubleshooting board but have now starting to infest and infect "Build it Yourself." In order to install an AR barrel, all you have to to is tighten a single nut until the notch lines up. But first, stick your new barrel in your upper receiver and make sure there's no play in the barrel pin notch and the front sight base is straight up and down. If it's not, take a jeweler's file and open up the notch to bring the front sight base up straight. You can tighten the notch to remove all slop (very important!!) merely but taking a small hammer and punch, and with the barrel in place very lightly peen down the threaded area on the "loose side" of the notch. Be careful, use very light taps because it doesn't take much!! Now that the front sight is straight, all you have to to is tighten one nut. I use a short (2-3 inch) stub of a gas tube in the bolt carrier key pushed into the upper receiver to keep the circlip, weld spring, and delta ring indexed. Spin the barrel nut on until it's hand tight, then lean on the barrel wrench until the next gas tube notch in the barrel nut lines up. If you're using the gas tube stub in the bolt carrier, you'll see it pop through the notch. That's it!!! STOP!! You're done!! Install the gas tube and handguards and go shooting!!! The whole process should take less than 20 minutes. If it takes longer, you skin your knuckles, or you have to loosen and tighten the nut more than once, you're doing it wrong!!!

Should you torque it 3 times too?  I've read that you should torque it once, loosen it, retorque it, loosen it and then the final torque should be over the 31 but not over the 80 to align the nut with the upper.  I believe that 'coldblue' wrote the USMC TM but I may be wrong.