Hello,
There is hardly any nut that will withstand the perpetual hammering of an air screw gun! Make sure that the socket is tight on the nut, soak for 1/2 hour with vinegar mixed with red transmission fluid if there is rust present. Some heat from an air blower can help as well. Also it sometimes makes things easier if you administer a heavy whack through a copper tube on the nut before trying to undo it. And also do not forget to say the magic words...
Good luck with your nut!
LATDOUGNUT