Midwest Industries New Professional Armorer's Wrench

[HKGuns]

I'll just add to this thread, since it is in the MI section that I think MI gets far too little attention as a producer of quality parts on this site.

I've used a bunch of their parts over the years and have NEVER had a single issue with any of them.

Something as simple as a sling swivel, if sourced from China, can be problematic and is pretty much a waste of money in my experience.

Their MLOK rails are extremely light and they're one of the companies who thought it through enough to eliminate the need to time the barrel nut for gas tube installation. Which in my limited upper building experience can be a PITA.

[Disciple]

On the clamshell the only rotational force on the barrel / barrel extension / index pin is friction from the barrel nut inner face on the barrel flange

What about the friction between the barrel nut and the receiver threads? That is going apply torque to the entire receiver which will press against the pin.

[pinzgauer]

What about the friction between the barrel nut and the receiver threads? That is going apply torque to the entire receiver which will press against the pin.

Nearly all of the torque is between the barrel nut threads and the receiver threads. The only force on the barrel is from friction between the barrel nut and the barrel flange which is fairly small. Especially if you correctly grease.

If you watch/measure carefully you can see that in a properly fitting barrel/receiver there is minimal rotation even in the index pin slot. A little bit of rotation of the barrel to take up slack between the pin and the slot is okay, but that friction force on the barrel is quite small relative to the overall torqueing.

[Disciple]

I must be misunderstanding the context. Are both the barrel and the receiver held in fixture while the nut is turned? If the barrel is fixed and the receiver is free to move, and torque is transferred from the nut to the receiver via friction the receiver slot will turn against the barrel pin, right?

[556Cliff]

I must be misunderstanding the context. Are both the barrel and the receiver held in fixture while the nut is turned? If the barrel is fixed and the receiver is free to move, and torque is transferred from the nut to the receiver via friction the receiver slot will turn against the barrel pin, right?

The only tools that fix both the barrel and upper are the MI-URR style rods, and to a lesser extent the Magpul BEV Block.

The part highlighted in red is correct for the standard Geissele Reaction Rod.

Many times you will see argument that when using the Reaction Rod the clamping force between the face of the upper and the rear facing surface of the barrel extension flange is strong enough to overcome the torque forces from being transferred through the receiver's barrel nut threads, which would force the upper against the indexing pin by way of the indexing pin notch... However, as seen time and time again in the many threads about sheared indexing pins caused by Reaction Rod use that's just not how it's playing out.

[pinzgauer]

After a decade plus of assembling uppers here's where I've arrived:

The clear majority of the torque is between the barrel nut and the upper receiver... I've seen it visually, and the physics makes sense as well.

Therefore it makes sense to clamp the upper receiver as the wrench is on the barrel nut.

This means one of many options:

- the traditional clamshell, which most of us tend to not like. And yet most of the really seasoned hands say it's still one of the best solutions for mil-spec sized receivers. IE: not billet or other oddities.

- The DPMS type nylon block that holds the upper receiver through the pivot pin holes. I know individuals who assemble a lot of uppers commercially and this is all they use.

If you know how to torque and end up on the lower end of GI spec by following the procedure or by using shims, this works well. I have one and it's pretty secure even though I question the stress on the pivot pin holes.

I would not use it for untorquing unknown barrel nuts that might be significantly over torqued or have loctite.

- The Bev block is an interesting compromise, and does the job. But allows more flex than what I would prefer. Which you could say "how does the Bev block flex as it locks both"? The issue is that the barrel does not move much, the receiver does. And there is enough slack in the fit to the receiver in most cases that it allows just a little bit of flex.

The MI tool might very well be the best of all worlds.

But based on my experiences I'm kind of wishing I just bought a good clamshell way back. Though I couldn't have used it on billet (sun devil) receivers, or it's more difficult.

Reaction rods and similar are useful for other things. I know all people using them in production environments due to speed, and I sort of understand that.

The bev block is very useful for holding receivers for work, etc in addition to torquing barrel nuts. It's a bit more fiddly, so I could see folks preferring other methods for production.

[Disciple]

Many times you will see argument that when using the Reaction Rod the clamping force between the face of the upper and the rear facing surface of the barrel extension flange is strong enough to overcome the torque forces from being transferred through the receiver's barrel nut threads, which would force the upper against the indexing pin by way of the indexing pin notch.

I follow now. The amount that the force on the pin was lessened would depend on the finish and lubrication of both the threads and the flange. This could explain why some pins shear and others do not. (lysander referenced that bolt thrust more than doubles with a lubricated chamber.) Now that I am aware of the possibility I would rather avoid the risk entirely with a better fixture.

- the traditional clamshell, which most of us tend to not like. And yet most of the really seasoned hands say it's still one of the best solutions for mil-spec sized receivers. IE: not billet or other oddities.

This is where I misunderstood; I thought "clamshell" meant the barrel vise v-blocks.

[556Cliff]

I follow now. The amount that the force on the pin was lessened would depend on the finish and lubrication of both the threads and the flange. This could explain why some pins shear and others do not. (lysander referenced that bolt thrust more than doubles with a lubricated chamber.) Now that I am aware of the possibility I would rather avoid the risk entirely with a better fixture.

Very possible, I know it's now a very popular practice by home builders to grease the entire barrel extension (rear facing side of the flange and all). Doing so would decrease the friction between the thread face of the upper and the extension flange considerably and could certainly be a contributing factor in Reaction Rod/indexing pin failures.

I've been told I'm clueless and that it makes no difference over on TOS for saying this by some of the "experts" over there, but the only place you should be applying grease is the upper receiver's threads and the forward/FSB facing side of the barrel extension flange. Those are the only sliding surfaces that absolutely must be lubed for barrel nut installation and I put a pretty liberal coating of grease on those surfaces... Not just a uselessly thin smear like I've see so many do. I also clean and degrease all parts prior to assembly to make 100% sure that the surfaces mentioned that could cause trouble don't have any lube on them.

I've never had a problem except for the one time that I forgot to grease the forward facing side of the barrel extension flange. I was using my favorite set of clam shell upper receiver vise blocks and it was a Brownells A1 barrel with a standard GI barrel nut... I noticed that I wasn't advancing on trying to align the nut on my way up to 80 Ft-Lbs, so as I backed the nut off one last time I heard a loud squeak! I knew immediately that I forgot to grease the forward side of the flange. I degreased everything and found a perfect DEEP imprint of the indexing pin on the left side of the indexing pin notch on in the upper receiver. So the notch on the upper (at least the left side) was toast, but the pin looked fine... So I switched to the Geissele Reaction Rod (all I had for action rods at the time) to get the upper to bias the index pin to the opposite side of it's index pin notch. Greased the correct spots (making double sure to get the forward side of the flange) and it torqued and aligned just under 35 Ft-Lbs... So lube on the forward side of the flange makes a BIG difference. However, that upper did require a lot of right windage to get it sighted in, probably due to the pin imbedding a bit into the right side of the indexing pin notch because the Reaction Rod doesn't support the upper against torque. Though I'd have to take it apart to find out and it's my brothers gun. I offered to replace the upper with a new one due to the f#ck up, but he hasn't taken me up on it yet.

[HKGuns]

I've been told I'm clueless and that it makes no difference over on TOS for saying this by some of the "experts" over there

You are in good company.

Hard to imagine some of those cats actually are trusted to own guns.

[556Cliff]

You are in good company.

Hard to imagine some of those cats actually are trusted to own guns.

Oh I know, it's a cringe worthy thought sometimes. The place draws a crowd that's all over the map and I think some of them might not know how to tie their own shoes.