Originally Posted by
MistWolf
Very carefully make relief cuts in the barrel nut that run parallel to the barrel. Cut deep enough that it will weaken the nut but don't go deep enough to damage the threads on the receiver itself. If you don't care about the saving the upper, you can cut all the way through. Start off with one or two cuts. You can add more cuts if the one or two don't work. If you have a barrel nut wrench with the pins on one side and what looks like gear teeth on the other and it's a standard barrel nut, use the gear tooth side of your wrench. The gear tooth side will give you more engagement surface on the nut. If you have not already done so, arrange the work so you are pushing up on the barrel nut wrench, not pushing down or pushing sideways, parallel to the floor. Pushing up lets you push against the floor. When pushing down or sideways, you only have your bodyweight to work with