How much torque does this nutt really need ?

or

Can you "REALY"  just tighten it down pretty good and make sure the lugs line up so that the gas tube goes through.

Ya me too...??
I have just tighted and then aligned the tube and never had a problem...

I just did this today with a friend. The book says 30lbs of torque for the barrel nut and you should tighten/loosen the nut three times before the final tightening.

We had the torque wrench all set up at 30lbs and did the 3x tightening and loosening and for the final we torqued it exactly 30lbs.... but then the gas hole wasn't aligned.

Hmmm so I gave it a big crank as far as it would go an voila! The holes line up. Though I am pretty sure it's torqued WAY past 30lbs.


In conlcusion, I wouln't worry about it.

I book says 30 ft/lbs, than in another spot it says no more than 80 ft/lbs I believe.  So anywhere from 30 to 80 should be fine.

Sort of depends on what type of AR you are building.

A service rifle grade with a standard barrel simply requires enough torque make it tight and to get the holes lined up properly.

A SPR or match grade AR, trying to stick to 30 or 35 pounds of torque will give you a little better accuracy.  Building an SPR with of a stainless steel barrel, for instance, you should try a few barrel nuts to find which one will get you closest to 30 when tightened. Going beyond 35 pounds or so on a match grade barrel will impart forces on the bullet that would go unnoticed or be unimportant on a service grade rifle.

Quoted: Sort of depends on what type of AR you are building. A service rifle grade with a standard barrel simply requires enough torque make it tight and to get the holes lined up properly. A SPR or match grade AR, trying to stick to 30 or 35 pounds of torque will give you a little better accuracy.  Building an SPR with of a stainless steel barrel, for instance, you should try a few barrel nuts to find which one will get you closest to 30 when tightened. Going beyond 35 pounds or so on a match grade barrel will impart forces on the bullet that would go unnoticed or be unimportant on a service grade rifle.

I have never heard of this before... source of info?

Gentleman behind the SPR program. He tries to target 35 pounds for the barrel nut, finds the best match of barrel nut and upper to do that, within reason. Usually about one barrel nut in ten will give you that 30-35 pounds, but if you can find that barrel nut, you'll be a bit better off.

Quoted: The GI spec and the Colt spec are very slightly different in text - but not at all different functionally. Colt spec is a min of 30ft/lbs USGI is a min of 31-34ft/lbs - not to exceed 80ft/lbs Which is to say the barrel nut needs to be torqued to a min of 30/31ft/lbs then aligned to the next slot to allow the gas tube to pass on center.  The respective barrel nuts also need to be taken past torque a min of 3 times for install.  They also require high temp grease for lube, and should never be moved counter clockwise to align the gas tube.

Thank you Paul!

Also, you guys might want to check out FALARAK's link tacked at the top of this forum: www.jobrelatedstuff.com/forums/topic.html?b=3&f=4&t=226782

A SPR or match grade AR, trying to stick to 30 or 35 pounds of torque will give you a little better accuracy. Building an SPR with of a stainless steel barrel, for instance, you should try a few barrel nuts to find which one will get you closest to 30 when tightened. Going beyond 35 pounds or so on a match grade barrel will impart forces on the bullet that would go unnoticed or be unimportant on a service grade rifle.

I'm having a hard time believing that the torque on the barrel nut has anythig to do with accuracy. I wonder if there is any hard evidence of this? I'd sure like to see it. It would seem that if this were true then there would be a difinite spec for torque - not 30 to 80 ftlbs!

Again, I'd sure like to see some documentation.

Quoted: A SPR or match grade AR, trying to stick to 30 or 35 pounds of torque will give you a little better accuracy. Building an SPR with of a stainless steel barrel, for instance, you should try a few barrel nuts to find which one will get you closest to 30 when tightened. Going beyond 35 pounds or so on a match grade barrel will impart forces on the bullet that would go unnoticed or be unimportant on a service grade rifle. I'm having a hard time believing that the torque on the barrel nut has anythig to do with accuracy. I wonder if there is any hard evidence of this? I'd sure like to see it. It would seem that if this were true then there would be a difinite spec for torque - not 30 to 80 ftlbs! Again, I'd sure like to see some documentation.

The USGI spec is for service rifles (30 to 80), where the accuracy gains are not significant or necessary. When tightening the barrel nut, you are applying torque 90-dregrees to the direction of bullet travel.  The effects of torque are slight on the lower end, but get greater and greater with the amount of torque.  After 80 pounds, you are twisting and likely damaging the upper and/or barrel extension (and barrel).  It's common sense, after 80 pounds you are likely either causing damage or getting close to causing damage, adding stress to the barrel/upper interface.  The more torque applied, the more stress applied.  The barrel nut does not need 80 pounds of torque to secure the barrel, it might need 80 pounds to get the barrel nut notch aligned for the gas tube.  Tighter is not better here. At 30-35 pounds, you have adequately secured the barrel into the upper.  Anything after that is about function (gas tube alignment), not barrel retention or accuracy.

Again, the effects are slight, but cummulative.  30-35 pounds on the barrel alone might not be noticed, but add to that a few other thnigs and you can get a noticable difference.  Add a good quality stainless steel barrel and you'll notice a big improvement in accuracy over a GI barrel right out of the gate (which tends to overshadow smaller potential gains elsewhere), but hit that target torque for the barrel nut and get a muzzle brake or flash hider to index properly at 5 pounds (using shims AND a crush washer, not just a crush washer) and you will have squeezed all you can out of that barrel installation.

This stuff isn't published (at least I don't think so), but it's being used out there.

All I know is that with a GI wrench you start to bend the teeth on the barrel nut somewhere over 39Ft-Lbs. and with a DPMS wrench you start bending teeth at around 25Ft Lbs. and when those teeth start bending that can't be good for anything else.

Quoted: Usually about one barrel nut in ten will give you that 30-35 pounds, but if you can find that barrel nut, you'll be a bit better off.

I'd better go buy a lottery ticket, as the last 3 uppers that I've barreled have fell in that range. I had two in which 30# hit the notch perfect with no additional tightening, and the other one just barely rubbed the gas tube at 30# and needed the barrel nut tweaked ever so slightly more.

Quoted: Quoted: Usually about one barrel nut in ten will give you that 30-35 pounds, but if you can find that barrel nut, you'll be a bit better off. I'd better go buy a lottery ticket, as the last 3 uppers that I've barreled have fell in that range. I had two in which 30# hit the notch perfect with no additional tightening, and the other one just barely rubbed the gas tube at 30# and needed the barrel nut tweaked ever so slightly more.

I wish I had that kind of luck. Last 2 barrels I've done where around 75/80Ft-Lbs.

awsome....Thanx guys

What does it mean to tighten it to the desired torque 3 times?

Do you tighten it to XX#, back it off and then repeat two more times OR just pull the wrench 3 times to the desired torque level?

I am about to do my first upper build so forgive me if this is a stupid question.  This is great information guys, thanks to all who contributed.

The Army Marksmanship Unit supposedly torques their flash suppressors to no more than 5 ft-lb because it can affect accuracy. Perhaps that is how Smith Enterprises comes up with the 30% gain in accuracy since you basically just hand tighten the Vortex.

Quoted: Quoted: What does it mean to tighten it to the desired torque 3 times? Do you tighten it to XX#, back it off and then repeat two more times OR just pull the wrench 3 times to the desired torque level? I am about to do my first upper build so forgive me if this is a stupid question.  This is great information guys, thanks to all who contributed. That is a good question.  It provides better thread fit. Take the nut to a torque of 31-35 ft/lbs and then back it off.  Then repeat again before you take it to the torque for the last time (and line up the gas tube slot). You will notice each time you take it to torque the gas tube alignment slot will move a tiny bit further clockwise.

I think it is also done to prevent a false torque reading. We're told to use moly lube for torque critical fasteners and to tighten/loosen the bolts a few times before finally torquing it down.

Quoted: The Army Marksmanship Unit supposedly torques their flash suppressors to no more than 5 ft-lb because it can affect accuracy. Perhaps that is how Smith Enterprises comes up with the 30% gain in accuracy since you basically just hand tighten the Vortex.

Hand tight plus red loctite for the AMU last I had heard.  Excessive torque on the flash hider can negatively affect accuracy.  Granted this is for the best of the best most accurate service rifles our tax dollars can buy!!  If I was building another service rifle for competition and it had a threaded barrel I would do it just like the AMU.

Quoted: I just did this today with a friend. The book says 30lbs of torque for the barrel nut and you should tighten/loosen the nut three times before the final tightening. We had the torque wrench all set up at 30lbs and did the 3x tightening and loosening and for the final we torqued it exactly 30lbs.... but then the gas hole wasn't aligned. Hmmm so I gave it a big crank as far as it would go an voila! The holes line up. Though I am pretty sure it's torqued WAY past 30lbs. In conlcusion, I wouln't worry about it.

Same thing happened here!

whatever you do, don't do it like Bushmaster did to my rifle!  I weigh 200lbs and I have sat on the armorer's wrench trying to remove the nut.  It's tricky and painful to sit on it but it can be done.  I also had to replace my workbench top twice because the strain put on it through the vise was so great that it broke.  Sadly I don't have any freezer space or compressed liquid nitrogen

Quoted: whatever you do, don't do it like Bushmaster did to my rifle!  I weigh 200lbs and I have sat on the armorer's wrench trying to remove the nut.  It's tricky and painful to sit on it but it can be done.  I also had to replace my workbench top twice because the strain put on it through the vise was so great that it broke.  Sadly I don't have any freezer space or compressed liquid nitrogen

Leverage man, leverage! Use a breaker bar with that armorer's wrench. Torque = force * distance from axis of rotation

If you increase the distance (longer bar aka cheater bar) less force is required to apply X # of ft-lb torque.

im just afraid of breaking the shelf I have it rigged to now.  I really need to rig it to a steel bar then take a hammer to the thingy.  I dont have a fancy bar to make it work but I do have a wood splitter and determination!  Poor barrel nut...