No Lock-Tite, it's just on by 70ish ft/lbs. I don't think any form of heating, freezing, or soaking in any kind of penetrating oil is going to solve your riddle.
Use an upper vice clamp, a Geissele reaction rod (or some form of internal barrel support) to stabilize along with a wrench and a rubber mallet to shock the nut loose.
You just need to overcome the torque of the nut.
IMHO, trying to use a steady pressure is just putting your upper and barrel at more risk of damage.