For anyone who has a postban fixed stock that they cannot got off because its lock tighted heres your solution. Take a dremul tool grind down two sides until you are almost or are to the threading of the stock. Then take a screw driver (flat head) put it under neath the ring and pry it up and off. Once you get it off goth sides just fall off. This is all done with minimal damage to the threading. And then all you have to do is install the new stock.

You can also use a "breaking device" which is a pipe to place over the wrench's end to give more leverage.  It'll pop loose in an almost crazy-easy way.

why don't you just drill through the center of the tube, and stick a rod (i.e. long screw driver) and use that as a lever?