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I hold upper receivers laying on their side in the vise of my milling machine. One "jaw" on the top of the Picatinny rail, the other on the surface where the upper and lower come together with snug with a layer of thin cardboard to not mar the surface. it's held very firmly and the upper can take a lot of torque. Of course remove the gas tube with the gas block from the nut and receiver before attempting to turn the nut. I then use a large strap wrench and some resin like used by gymansts and weight lifters between the strap and the tube. You can apply around 200 ft-lbs torque to the barrel nut which is often affixed to a free-float tube. Put the strap at the nut end. A heat gun will help whehter there's some adhesive or not. Apply heat to the nut and not to the receiver so the nut will expand more and loosen it. I've never had one which didn't respond properly but thy can be pretty tight. The nuts are supposed to be tightened between 30 and 80 ft-lbs Whatever in between to make the gas tube line up though a hole in the nut and the receiver. That range may not be quite enough to move one hole. which can require removing a bit of metal from the receiver or barrel nut, or adding a shim.
Get a good strap wrench with at least a 1 foot handle. They come with plastic, cloth, or rubber straps. I've had best luck with the "Rigid" brand with a 1" wide plastic strap. They're available at most plumbing stores . Don't use the kind with a chain and vise grip. They''ll take off the handguard but tear it up in the process. The resin looks bad but washes off.
Last edited by LouBoyd; 05-08-2010 at 05:07 PM.
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How to heat
Linear Mode
