BCG very tight, crushed receiver?

[ar15barrels]

Just wondering why/how would it trash a receiver?? it mates up to the steel extension on the barrel which is torqued at a much higher value than the barrel nut and the force you're putting into the receiver is minimal. If anything, you're putting some force on the indexing pin which is pushing on the notch cut into the upper receiver... but if you're getting to an amount of force where you sheer that off you probably shouldn't be working on your own stuff. I've seen many MANY more horror stories of the vise based polymer clamps/blocks cracking receivers due to it not holding firmly, etc. I would think the reaction rod would be less desirable for muzzle devices because the rotational force imparted into the barrel/pin when putting on the device instead of the torque put into the upper threads/barrel shoulder when torquing on the nut.

If you hold the barrel extension with a reaction rod and torque a barrel nut to a receiver, ALL of the torque is transferring from the receiver threads, THROUGH the indexing pin to the barrel extension to the reaction rod.
So, you are putting a lot of torque on the index pin and it would be easy to damage the receiver at the recommended 30-80 ft-lbs of torque.

When you hold the receiver and torque the barrel nut, the torque on the barrel nut threads is not going to be turning the index pin in the receiver.
The force on the barrel extension flange will be clamping MUCH more than it will be turning.

The reaction rod works great for installing muzzle devices because all the torque on the barrel will be through the barrel extension with NO torque on the index pin or the receiver.

[cgates]

If you hold the barrel extension with a reaction rod and torque a barrel nut to a receiver, ALL of the torque is transferring from the receiver threads, THROUGH the indexing pin to the barrel extension to the reaction rod.
So, you are putting a lot of torque on the index pin and it would be easy to damage the receiver at the recommended 30-80 ft-lbs of torque.

When you hold the receiver and torque the barrel nut, the torque on the barrel nut threads is not going to be turning the index pin in the receiver.
The force on the barrel extension flange will be clamping MUCH more than it will be turning.

The reaction rod works great for installing muzzle devices because all the torque on the barrel will be through the barrel extension with NO torque on the index pin or the receiver.

This is what the description of the reaction rod says

"The removal and installation of barrels, flash hiders, gas blocks and hand guards is made much easier and simpler. The Reaction Rod is designed to be gripped in a bench vise so that the rod is either horizontal or vertical. The upper receiver is then slid onto the rod and the rod’s integral splines enter the barrel extension and secure the barrel extension from turning. This allows all the torque from barrel nut wrenches to go directly into the barrel extension. In contrast, receiver vise blocks transmit the turning force into the aluminum receiver, a good part of which passes through the small, easily distorted receiver index pin. With the Geissele Reaction Rod, marring of an upper receiver’s finish by gripping and twisting inside vise blocks is eliminated and so is the need to remove sights and mounts from the receiver’s M1913 rail."

These two descriptions are in direct opposition to each other. One is right, and one is wrong.

[akjunkie]

The right way to use your torque wrench is to set it to 30, go until it clicks, then set it to 80 and go until the next notch.
Then, if it clicks before you reach the next notch, you know you need to stop and get shims instead of just going to the next notch...
By NOT setting the wrench to 80, you can pass right through 80 while simply going to the next notch.

Wow..good tip!
Thx Randall.

[ar15barrels]

These two descriptions are in direct opposition to each other. One is right, and one is wrong.

Think about what is happening when you are tightening the barrel nut against the threads of the receiver.
It's pretty easy to determine where the torque really is going.
The threads have far more surface area (resistance to torque) than the flange of the barrel extension so the receiver and barrel nut are generating and bearing the vast majority of the torque that you are applying with a wrench.

The key to assembling parts without damaging them is simply managing where the torque is going.
No tool is right for every job.
You need to use the right methods and tools for EACH job.

[NewbieDave]

I've seen Randall work... take his word for it, he knows his stuff. 'Nuff said...

[SFCRangerDoc]

Randall, ok that makes sense... I'm still a little unsure how the 80ft lbs max could break the steel indexing pin but I'll run with that.

Since you're the local resident pro on all things AR, etc...is there a receiver block/clamshell that you recommend for upper building other than a reaction rod? There are so many flavors of upper clamps, etc all with mixed reviews saying OMG BEST THING EVER or OMG THIS F*CKED MY UPPER UP.

FWIW I rebuilt an mp15 upper (free float MI handguard, etc) with the brownells tool w/out issue and ended up with a final torque value of somewhere between 68-70 Ft/lbs and didn't feel like i was over stressing anything.

[isplice]

It won't break the steel indexing pin. The receiver will begin to rotate, and the pin will begin to deform the indexing pin channel in the upper receiver. You could end up with the barrel rotating slightly, then wondering why you have to put in so much windage at the range to zero your rifle.

[ar15barrels]

Randall, ok that makes sense... I'm still a little unsure how the 80ft lbs max could break the steel indexing pin but I'll run with that.

is there a receiver block/clamshell that you recommend for upper building other than a reaction rod?
There are so many flavors of upper clamps, etc all with mixed reviews saying OMG BEST THING EVER or OMG THIS F*CKED MY UPPER UP.

It's not an issue of BREAKING the pin, though that does happen occasionally.
The main issue is the pin PRESSING into the side of the indexing notch, causing the barrel to rotate out of alignment with the receiver.
This is primarily an issue on guns with a front sight base affixed to the barrel.
Users with gas blocks and freefloat rails will seldom care if the barrel is 2 degrees out of alignment as the users won't even notice the damage that occurred during assembly.

I have a bunch of different receiver blocks and I choose from them according to the job at hand.
My go-to block is the DPMS claw, so much so that they both (small & large sizes) live on my bench next to the vise.
All my other vise blocks live in drawers.
The DPMS claw is great under 60 ft-lbs.
Approaching 75ft-lbs, it starts to flex so I put it away and move to a pair of PRI aluminum blocks and the receiver gets clamped in the milling machine vise BETWEEN the two blocks (one on the rail, one on the bottom).
This setup is good for 150+ ft-lbs without breaking a receiver.

The people breaking receivers on plastic blocks are exceeding the torque that they should be using the block UPRIGHT for.
You can exceed 100 ft-lbs safely on the plastic blocks if you simply turn the receiver sideways in the vise and put a piece of wood on top of the rail so that you are clamping the rail on both the top and the bottom.

[SFCRangerDoc]

Interesting...I get ya now on what part actually gets damaged. I don't feel like there was any play between the pin and the reciever when i disassembled mine a second time after realizing i needed a shim in there so I guess I got lucky on it.


Also, thanks for sharing your tool preference!

I looked at the PRI block and thought it might be worth getting at some point. Using them in a paired configuration is a damn brilliant idea too. Guess I'll have to invest in a couple more tools!

[ar15barrels]

I looked at the PRI block and thought it might be worth getting at some point.
Using them in a paired configuration is a damn brilliant idea too.

The ONLY way I would use the PRI block is in a paired configuration.
If you try to torque a barrel nut with the receiver upright and just two pins through the bottom of the receiver, you are asking for trouble.
The reason the DPMS claw works so well is that it is supporting the inside of the receiver as well so that none of the force of barrel nut installation is transferring to the two pins.

[SFCRangerDoc]

The ONLY way I would use the PRI block is in a paired configuration.
If you try to torque a barrel nut with the receiver upright and just two pins through the bottom of the receiver, you are asking for trouble.
The reason the DPMS claw works so well is that it is supporting the inside of the receiver as well so that none of the force of barrel nut installation is transferring to the two pins.

this is all incredibly good knowledge. I plan to build some more uppers and I think i'll definitely invest in the DPMS first and then a pair of PRI blocks later on if I feel I need them.

[EVGRambis]

Good information ar15barrels! Thank you braddah!

What do you guys think of the Magpul BEV block? Is it good to go or should one get a clam shell or DPMS claw type? Looking into the PRI block it seems to be discontinued.

EDIT: scratch that... I found it available directly from PRI.