on mine, it was a royal pain in the butt. i couldnt get the darn thing off to save my life, with the ole' screwdriver through the windows trick.
what i wound up doing, is cutting the front half of the flash hider off where the windows are the biggest, then cutting a slice in the fh parallel with the bore, the length of the metal. i was able to get it almost paper thin without getting into the threads on the barrel, and then careful application of a hatchet and 32oz ball-pein (the only wedge shaped tool and striking implement handy) into that cut gave me enough of an advantage to smack the thing loose. a couple rotations counter clockwise with the hatchet and hammer, and it came loose by hand. good luck, youre gonna need it!!
oh yeah, get some mapp gas or propane. hot things tend to loosen more easily.