ok, last night im building an M4 upper and on the first pull i took it all the way to 51# at which point my 75yr old vice broke. the blocks and barrel tumbled out leaving some nice metel smears on the barrel. luckily they will be covered by the handguards. i was not able to back it off and re-torque three times as instructed by the military. by sheer luck the barrel nut was properly indexed when the vice broke so i chose to leave it. i finished assembly, checked headspace and took it to the range today. it was a stellar performer sampling Q3131a, clean and shiny Guat, santabarbara, M855 and even a little Wolf totalling about 300rds.

could any long term damage result from being improperly installed? more importantly could a dangerous situation result?

Woa I didn't even notice the 3 time torqueing (maybe that will get mine to the next slot on the barrel nut).  

The SPEC IS 31-35ft lbs. (a la MARINE corps manual (I don't know why but I have never seen an Army manual I think we might use the Marine manual too.)

[b] as a side note.. how did your rifle group with WOLF ammo? was it 55gr or 62gr? whats your barrel twist[/b]


SLOW IS SMOOTH, SMOOTH IS FAST

BTT

If anyone thinks the 31 to 35 foot-pound spec is actually going to WORK on all M16's, they're more optimistic than anyone I know!

The spec should actually be stated as "whatever it takes to properly align the barrel nut lugs so the gas tube passes through the upper receiver properly, as long as that figure is at least thirty foot-pounds and no more than eighty foot-pounds."

At least 30, not more than 80, and whatever it takes to install the gas tube.

It's the strangest torque spec I've ever heard of.

CJ

im asking about the 3 times torque. i was only able to get to torque it one time. what kind of problems can this cause long term??? also i went rather lightly on the anti-sieze.

No harm, I just went through USAF Combat Arms training (basically USAF gunsmithing school). The 3 times rule is only to guarentee that the Moly B was worked into the threads as much as possible.

No problem really.

Troy, JAR thanks alot. i was kinda stressing this. i tried calling the 2112 in our unit and i cant get him to answer his cellphone. i think i went a little too light on the Moly, i guess we'll find out if i ever try to remove this barrel.  thanks again.

Since I'm the former Marine that came up with the 3-times torque, let me say you are ok.  Even with just a little grease.
If it ain't broke, don't fix it.
ColdBlue sends...

Your unit armorer must be better than ours (he is afraid to tighten buffer tubes and buttplate screws)<"because, they need to be tightened by a certified armorer"


I would like to say

IT'S NOT VOODOO TIGHTEN THE DAMN BUFFER TUBE !

but he is a mental retard and is doing it the Army way (fill out the form and send the gun to HQ and they tighten the tube{with the same tools as we have} and send it back in a couple of months.)

ColdBlue,
 youre blessing eases my troubled mind. thanks for chiming in...so why did you specify 3 times torque???

DvlDog - God loves you if your vice broke with the hole aligned. [:D]

ColdBlue - if you're the man who came up with the procedure -  that's cool!  "Thanks" from every AR15/M16 guy out there!

The Airforce manual calls for 35 ft, lbs., the Army calls for 85. The Airforce and USMC are correct. Wherever the Army got there info. is beyond any rational, but the Airforce were the proponents from the beginning and didn't have to contend with Picatinny. 85 ft.lbs. can damage a receiver, and has on a few occations.
Three times at 35lbs doesn't hurt anything and just assures it's on the money as long as the gas tube goes thru without touching anything it shouldn't.
Good shootin, Jack

GreenO, our unit armomrer is an E7 who is a 2112 from quantico. those are the guys who build M40's MEUSOC pistols DMR rifles etc. these guys are not parts changers. we're talking old school gunsmith/machinists. if you can ever get him to answer his damn phone.  he told me the spec was 35-80lbs the wide spread having to di with the moly affecting the sheer loading of the threads. he also told me he's seen recievers break around 65# so 51# was good enough for me.

and yes, someone must love me. the nut was indexed almost perfectly.

The Army manual is TM 9-1005-319-23&P, is the standard one and is also used by the Air Force (TO 11 W3-5-5-42). (since they both adopted the rifle before the Corps is stands to reason the would have an Armorers manual - besides where do you think the USMC sends it armorers to for training?  Hint: its an ARMY facility located in Maryland [;)]).

On page 3-42 of the manual (change 3) it states

I only have up to change 3 at work on a .PDF, my more recent copy (to change 6 or 7) is at home - contact me offline if you want me to check to see if they put an upper spec in the newer manual.

Jack,
Where are you getting your info on the Army's spec.  I've got the manual sitting here in front of me and I just quoted out of it (see above).  I've seen NOTHING for 85ft-lbs nor anything for 85in-lbs.

Same with the Airforce - thier spec is the same as the Army's (it the same Darn Manual), min of 30 ft-lbs but you can go more to align the nut.

Yep, the Army and Air Force publish a joint manual:  ARMY TM 9-1005-319-23&P AIR FORCE TO 11W3-5-5-42.  Here're some extracts:




-- Chuck

My first Ordnance Officers assignment after Viet-Nam and then OrdOff School at Quantico was with 1st Maint. Bn at Camp Pendleton.
I worked with CWO Gordon Kampen at the Small Arms Shop at Las Pulgas.
During this period we re-barreled every M16 in the 1stMArDiv to cull out the non-chromed chamber and barrels.  So like we did thousands or re-barrels over a period of months.
I don't remember who in the shop started doing it, but the two pre-torques were found to help get you to the next notch if you initial 35 or so was way too short of the next notch.
We did not have some of the improved barrel nut wrenches and PeaceRiver Arms receiver blocks available today.  So anything past 40 or so caused the barrel to rotate in the original aluminum vice jaws.  Often, another Marine would resist the torque with a breaker bar through the front sight "A" frame, often resulting in the wrench slipping off the nut and damage occuring.  So we were confident that we were putting enough torque to the assembly.
Unfortunately, "lessons learned" from shop practices like this don't end up in reprints of the TM.    
Years later when I had charge of more than 2,600 M16A1's at Quantico which had seen years of hard use, lose barrels were a problem.  You could actually feel that the barrel nut was lose, and how it "loosened" with a gas tube passing through it is still bit of a mystery.  However, I remembered the two pre-torques from Pendleton, so we tried that to repair the rifles with the problem using that method and it worked fine.  
But very often, when this rifle went to the range, it was found to have "excessive windage".  We eventualy discovered a relationship to rifles with "loose" barrels, and upper receivers with alingment slots way over the .125" spec.
So I think there were two forces at work here, (1)the bullet tearing down the barrel about 6,000 times at 50,000 psi, tends to pull the barrel to the front, streching the upper aluminum receiver threads via the steel barrel nut, and (2) the right-hand twist transmitted to the barrel alignmnent pin (steel)in the upper receiver slot (alum) tends to widen this slot, causing the front sight to cant...so excessive windage.
When I had the oportunity to revise both the A2's Operator and Technical Manuals, I tried to put in as many of these lessoned learned as possible in the text.
Compare an original A1 Army Operator's Manual with the USMC's M16A2 (camo cover) and you will see lots of these from cleaning techniques to loading alternating tracers.
ColdBlue sends...