Yup, I am aware of this. I got the one on my shorty off easy enough with the welds. I can't seem to even move the castle nut on this one though.
Get a soft face hammer and give the flash hider a few hits from the front. That will take some of the load off the castle nut. Hungry and I had to do this to get mine to budge. Support the barrel and don't be afraid to give it a good whack. Worse comes to worse, it breaks around the spot welds and you need to buy a new flash hider.