Clamp down the upper, use a proper armor's wrench with a extension. If the delta ring is factory tighten, the shim they use could be crushed and wedge the barrel nut to the threads of the receiver. If that's the case, only way to remove the delta ring is to cut it. No torquing or heating will remove it without cracking the receiver. Look down into the gap between the barrel and barrel nut. If you see a shiny piece of metal, that's the shim. If it's deformed than it's wedged.
Here's my post on how to clamp and removing the barrel nut.
http://airsoftcanada.com/showthread....ght=barrel+nut