Disassemble the outer barrel/front sight/flashhider assy. and stick it in the freezer for like an hour or so, then try again (might wanna use work gloves). Heating expands the metal and makes it tighter != good.
Clockwise == turn from left towards the right
CCW == turn from right towards the left
You want to be turning CCW.
I've done this successfully on a lot of overtightened stuff.
If you really must, wrap the FH in a towel and use a vise grip on the "flat" parts at the base of the flash hider. That'll give you more torque. Combined with freezing it should come off, unless it was epoxied in place or something.
__________________
|