I tried every trick you listed and then some but it would not break loose. Been doing this for over 40 years and never saw one like this one.For the stubborn nuts....I've gotten everyone off by doing this. Wheeler action wrench, take and put action and wrench in my 6" Wilton vise.Doubled up nut wrenches taped together , 4 pound dead blow hammer. Works everytime. Matte and blued finish barrels and actions new. One more thing I let a good penatrating oil soak in for a couple of days from the flange end of the nut. The more bluing salts in there the tougher they are to get off.