Help!! My A2 flash hider won't set properly....

[LRRPF52]

Not to completely hijack your thread, but how do you set a barrel in a vice as opposed to the upper? It makes sense why you would do this (to avoid warping the upper when torquing, I suppose), but I'm not clear on how to vise the barrell tight enough to torque without scarring the barrel.

I know, newbie shining through...

This is an important question. The reason for clamping the barrel and not the upper is that if you clamp the upper, you will be torquing the barrel and barrel extension, which you don't want to do. The barrel itself must be clamped in the vice very tightly, with insulating blocks. I personally use the resin-type rubbery blocks with magnets that hold them in your vice jaws, and they have channels in them for tubulars and angles as well. You do have to crank down on the vice to get a secure hold of the barrel, or it will slip.