Install flash hider - clamp on upper or barrel?

[Tango24]

I am assembling a new upper. I am trying to figure out how I will secure the upper while tightening the flash hider. Is it better to use a barrel clamp in a vise or to use the upper receiver block and clamp it from the upper? Thanks for your thoughts!

 

[Ballista One]

Always the barrel...

 

[Tango24]

Can the barrel nut also be tightened while clamping the barrel?

 

[mallrat]

Should be

 

[Ballista One]

Can the barrel nut also be tightened while clamping the barrel?

Not a good idea. There is a chance you will shear the index pin on the barrel extension.

This the reason the Reaction Rod and other tools like it are a bad idea. You always want to fixture one of the parts being joined.

 

[Tango24]

You always want to fixture one of the parts being joined.

I'm not sure I understand. If the clamp is on the barrel and I'm turning the barrel nut isn't that one part being fixed in place?

 

[wareagle700]

Not a good idea. There is a chance you will shear the index pin on the barrel extension.

How so?

 

[bp7178]

By drastically over torquing...

 

[GH41]

Tightening the barrel nut holding the barrel/extension with a reaction rod is ideal but many are tightened holding the receiver in a block. Install the MD with the barrel clamped as close to the muzzle as possible.

 

[wareagle700]

By drastically over torquing...

Obviously.

I've seen receivers crack but never the steel barrel extension pin sheer off. That takes talent.

 

[Ballista One]

I'm not sure I understand. If the clamp is on the barrel and I'm turning the barrel nut isn't that one part being fixed in place?

When possible, you always hold one of the threaded parts and turn the other. The barrel isn't one of the threaded parts. In this case, the receiver and the barrel nut are.

How so?

When the barrel is clamped and torque is applied to the barrel nut, the receiver can rotate on the barrel extension. The index pin is the opposing force. 7075-T6 is harder than a bulls balls and it'll slice through the index pin like warm butter.

 

[HD1911]

Geissele Reaction Rod... safest way to do it.

Handy for Barrel, Muzzle Device, and Gas Block R&Rs.

http://geissele.com/tools/reaction-rod.html

 

[corym468]

I use a reaction rod for muzzle devices. I clamp the upper receiver to torque the barrel nut.

 

[Tango24]

When possible, you always hold one of the threaded parts and turn the other. The barrel isn't one of the threaded parts. In this case, the receiver and the barrel nut are.

Thanks, I see what you meant now. So I need to clamp the upper receiver while tightening the barrel nut. Is this the weakness then of the reaction rod, that it doesn't grip either the barrel nut or the upper receiver? As I understand it, the reaction rod only grips the barrel via the barrel extension.

I guess that means I need two tools, the upper receiver clamp and the barrel clamp for the vise.

 

[Ballista One]

I guess that means I need two tools, the upper receiver clamp and the barrel clamp for the vise.

I you want to do it right, yes.

 

[HD1911]

Thanks, I see what you meant now. So I need to clamp the upper receiver while tightening the barrel nut. Is this the weakness then of the reaction rod, that it doesn't grip either the barrel nut or the upper receiver? As I understand it, the reaction rod only grips the barrel via the barrel extension.

I guess that means I need two tools, the upper receiver clamp and the barrel clamp for the vise.

No. Why would securing the Upper via Reaction Rod inserted into the Barrel Extension, which is Torqued onto the Barrel at around 150 Ft. Lbs., take a Back Seat to Clamping an Upper Receiver, that is going to Flex and at the Same Time, allow the Index Pin to be stressed, when applying Torque to the Barrel Nut?

Think: Axial Force and Concentric Loading

 

[Ballista One]

No. Why would securing the Upper via Reaction Rod inserted into the Barrel Extension, which is Torqued onto the Barrel at around 150 Ft. Lbs., take a Back Seat to Clamping an Upper Receiver, that is going to Flex and at the Same Time, allow the Index Pin to be stressed, when applying Torque to the Barrel Nut?

Think: Axial Force and Concentric Loading

I've thought through this tool enough times to form an opinion on it and it's not the best tool for the job. What prevents the receiver from spinning on the barrel extension when applying torque to the barrel nut?

 

[mallrat]

I've thought through this tool enough times to form an opinion on it and it's not the best tool for the job. What prevents the receiver from spinning on the barrel extension when applying torque to the barrel nut?

The index pin. If you shear the index pin while torquing the barrel nut, either you're applying too much torque or the index pin was a flawed part to begin with. Likely both.

 

[Ballista One]

The index pin. If you shear the index pin while torquing the barrel nut, either you're applying too much torque or the index pin was a flawed part to begin with. Likely both.

Go away... quietly. Thank you!

 

[g3ninfinite]

How To Install a SureFire Flash Hider - YouTube

I dont promote any specific way but heres a nice video.

 

[Tango24]

Great, thanks everyone! Just to check in, what I understand know is either the upper receiver clamp or the Reaction Rod would work just fine for installing the flash hider. I haven't purchased the upper clamp yet but the price of the Reaction Rod will probably know that one out of consideration for me.

g3ninfinite,
Thanks for the video. There was one comment that worries me. He said that the flash hider should not be torqued more than 30 ft-lbs or else you could end up with barrel distortion. The flash hider I have is a standard A2 and am putting on a WOA SPR 18" barrel. This barrel is thicker than the standard 0.75", it measures 0.851" thick. The issue is that my flash hider (with a crush washer) will need quite a bit of turning to line up properly. Should I be concerned about how much I will need to torque it?

 

[LRRPF52]

I'm surprised they used that receiver insert with the cross pins in the video. I've seen several uppers destroyed with them. I also prefer to isolate the barrel when doing muzzle device work, so I clamp the barrel in the vice with inserts. At such low torque, he was ok. It never made sense to me to put rotational load on the upper receiver lugs with cross pins inside them.

The armorer's technical manual shows clamping the barrel for both muzzle device and barrel nut work.

http://imagizer.imageshack.us/a/img802/3477/barrelviseblockmethod.jpg

If you are timing an A2 flash hider, and a crush washer doesn't work within the torque specs of 20-30ft-lbs, you need to shim it with a proper set of shims. Don't go Captain insano on torque with the muzzle device.

 

[Tango24]

I purchased both the flash hider and crush washer from White Oak. They've been great on the phone and provided a lot of help along the way while I was researching parts for this build. Once the flash hider is finger tight it is about 3/4 turn away from where it needs to be. That strikes me as a lot of turning that needs to be done. Hopefully the torque required for that amount of turning will not exceed the ~30ft-lbs discussed. this will be one of the primary needs for me to secure the barrel in a vise. The other will be to secure the barrel nut.

 

[corym468]

Thanks, I see what you meant now. So I need to clamp the upper receiver while tightening the barrel nut. Is this the weakness then of the reaction rod, that it doesn't grip either the barrel nut or the upper receiver? As I understand it, the reaction rod only grips the barrel via the barrel extension.

I guess that means I need two tools, the upper receiver clamp and the barrel clamp for the vise.

Gripping the barrel extension is fine. The barrel extension puts an order of magnitude more torque on the barrel than a muzzle device should ever at max torques.