Hence with the insert in the upper receiver so the vise block will not crush it, the clam shell upper block in a vise on a sturdy bench, have yet to come across a barrel nut that will not spin off a upper, even without having to resort to a cheater bar on the barrel wrench.

Hell most of the time, I just end up tearing down and building the upper receiver on the mill, since it allows me to double check down the upper receiver line , then check the Barrel gas port to make sure it TDC/ the barrel is not canted off to one side, and then rough adjust the DCM adjustable FSB to get them close for final sight in as well.

The ops rig being Ruger factory built, does not have loctite used during the build, and no heat is needed to break it down.

Hence the heat marks you see on my block, is from tearing down CMP rigs to re-barrel them , and where loctite is used on this rigs instead.