What do you put on barrel extensions?

[One More Time]

I don’t think I would call moly lube non-metallic, but I also don’t know if it matters.

It's Loctite I was referring to not Permatex and it is a metal free anti-seize.
Regular anti-seize is a whole lot cheaper though.
https://www.grainger.com/product/LOC...IaAtqlEALw_wcB

The stuff for Detroit Diesel head bolts/main cap bolts is an even lower friction paste.
Used on 3/4" bolts and larger, smaller bolts will shear off before torque is reached.

[556Cliff]

I don't think it is correct. Action and reaction. The barrel nut mates with upper receiver. When the nut is torqued, there must be equal and opposite torque (minus thread friction) applied to the upper to keep it from turning. The question where is that counter from.

Clamping the barrel, including action bar, the counter torque comes from the index pin. Not good. Clamping the upper. The origin of the counter torque is obvious. Definitely not through the pin. Good.

I understand the army manual specifies clamping the barrel. For what I don't know. But it doesn't make sense. As an employee of a defense contractor, I worked with government officials on occasions. Despite their technical titles, not all of them know what they are doing.

-TL

Sent from my SM-N960U using Tapatalk

That's what I don't get. Though lysander does indeed have the mathematical numbers to back up what he's saying. The weird thing is that it has not actually panned out through people's experiences actually using the standard/fin-less Reaction Rods. Either there are too many variables at play that can't be accounted for with guys either lubing things that shouldn't be lubed, or not lubing things that should be lubed, or something is being missed completely by the math.

[One More Time]

That's what I don't get. Though lysander does indeed have the mathematical numbers to back up what he's saying. The weird thing is that it has not actually panned out through people's experiences actually using the standard/fin-less Reaction Rods. Either there are too many variables at play that can't be accounted for with guys either lubing things that shouldn't be lubed, or not lubing things that should be lubed, or something is being missed completely by the math.

Turning the barrel nut cannot turn the barrel, it is held by the vise, however it can turn the upper, but only through the friction from the greased threads, which is relatively small. Because the transmitted torque is small, the load on the index pin is minimal.

That I believe is key phrase.
Over torqueing will get things moving enough to potentially damage it.

When the upper is secured lubing all contact points is needed to keep from friction locking it.

[1168]

Lubrication of threads allows for higher clamping loads for the same applied torque, as more of the torque is used to stretch the bolt rather than overcoming friction.

Over time, the oil in grease or anti-sieze evaporates off, giving you and unlubricated joint. Because the clamping force is higher, it will take more torque to loosen. (You might see what appears to be grease residue on the bolt, but that is just the thicker, the oil has boiled off.)

thanks.

It's Loctite I was referring to not Permatex and it is a metal free anti-seize.
Regular anti-seize is a whole lot cheaper though.
https://www.grainger.com/product/LOC...IaAtqlEALw_wcB

The stuff for Detroit Diesel head bolts/main cap bolts is an even lower friction paste.
Used on 3/4" bolts and larger; smaller bolts will shear off before torque is reached.

the stuff at that link says non-metallic, metal-free, moly, and molybdenum. Molybdenum IS metal. That’s all I was saying.

[One More Time]

Molybdenum IS metal

True.
Moly or Molybdenum disulfide is kinda like graphite though.

[lysander]

thanks.

the stuff at that link says non-metallic, metal-free, moly, and molybdenum. Molybdenum IS metal. That’s all I was saying.

Molybdenum is a metal, molybdenum disufide is not a metal. The same way that sodium is a metal, but table salt (sodium chloride, NaCl) is not a metal

[1168]

Molybdenum is a metal, molybdenum disufide is not a metal. The same way that sodium is a metal, but table salt (sodium chloride, NaCl) is not a metal

Somewhere, a Chemistry teacher weeps at my ignorance.

[lysander]

That's what I don't get. Though lysander does indeed have the mathematical numbers to back up what he's saying. The weird thing is that it has not actually panned out through people's experiences actually using the standard/fin-less Reaction Rods. Either there are too many variables at play that can't be accounted for with guys either lubing things that shouldn't be lubed, or not lubing things that should be lubed, or something is being missed completely by the math.

Not lubricating the flange will decrease the clamping force between the nut and the upper for the same torque, as more torque is expended overcoming the friction between the nut and the flange. Because there is an increase in clamping force with the grease, there will be an increase in torque transmitted through the threads, and an increase in the load on the index pin.

Something not reported is going on here:

I have accidentally put enough torque into a barrel nut to break it and not damaged the index pin notch that much. (By the book lubrication)



If you clamp the barrel, don't grease the flange, if you clamp the upper, grease the flange. If you clamp both, it doesn't matter.

People don't seem to believe it, but most engineers who write manuals have a reason for writing the instructions the way they do.

[556Cliff]

Not lubricating the flange will decrease the clamping force between the nut and the upper for the same torque, as more torque is expended overcoming the friction between the nut and the flange. Because there is an increase in clamping force with the grease, there will be an increase in torque transmitted through the threads, and an increase in the load on the index pin.

Something not reported is going on here:

Nothing I can think of has been left out as to what caused the indexing pin to become embedded into the left side of the indexing pin notch on that particular upper. My own curiosity to figure out what the cause could have been had me recounting the procedure pretty meticulously to realize what had happened. But really, my first clue was the loud squeak! When I loosened the nut.

The set up for the damage that you see in that picture was with clam shell upper receiver vise blocks (the old Bushmaster ones that are hinged at the bottom), held in a solidly secured Wilton Bullet Machinist Vise. Lube used was Brownells Barrel Assembly Paste (65% moly content) applied very liberally to the threads of the upper receiver (but regrettably not the forward side of the barrel extension flange). Standard torque procedure as laid out in the TM was followed with a barrel nut wrench that copies the same dimensions for drive slot center distance as on the GI 3 pin armorer's wrench (2UniqueLLC). Snap-On Torque wrench that was well within calibration specs was used up to almost 75 Foot Pounds (which is the full range of the wrench). The reason I stopped and backed off the nut was because the nut was not advancing at all for gas tube alignment as the nut was friction bound on the dry barrel extension flange. So as far as I can figure the only thing that caused it was the lack of lube on the forward side of the barrel extension flange.

The upper is a Brownells A1 upper, which should be forged 7075 with type 3 hardcoat anodizing. But without sending the upper off for metallurgy testing I can't state that for a fact.

Now after that mess with the indexing pin pressed into the left side of the indexing pin notch, of course the FSB was out of alignment. So after I took everything apart and hosed all grease off of all the parts using non chlorinated brake cleaner. I greased everything back up (including the forward side of the barrel extension flange this time) and reassembled using the Geissele Reaction Rod to be sure that the indexing pin would bias to the right side of the indexing pin notch to hopefully keep the FSB centered. The same torque procedure was followed and I had gas tube alignment at 30 Foot Pounds (same barrel nut). But now the FSB was canted left due to the indexing pin embedding into the right side of the indexing pin notch due to the unsupportive design of the Reaction Rod... But the major takeaway from that experience is that greasing the forward facing side of the barrel extension flange does indeed make a major difference in advancing the nut for alignment.


Since that upper (2016 I believe) I now have a much better method for barrel installation and removal that uses both the clamshell upper receiver vise blocks and one of a few fin topped Reaction Rods in tandem in a way to mechanically lock both the upper and barrel together to where no damage can occur to either the indexing pin or indexing pin slot. Similar to having both parts (upper and barrel) secured in their own vise to prevent them from moving. Haven't had any issues since.

Of course (unlike the standard Reaction Rod) the fin topped Reaction Rods should be fine to use by themselves for barrel installation, but I'm still leery of it to some degree.

[lysander]

Could be that the aluminum wasn't tempered correctly . . .