A strap wrench available at Sears among other hardware stores.  That will get the grip without damaging the neck.  (Of course you can make one of these yourself too.  Not hard.)  You'll probably want to put a drop of two of loctite on the threads when you change it out to keep it set.  The hopper gives a good bit of twisting torque and I have found mine unscrewing mid game if getting bumped about.

i use an old leather belt wrapped around it and put into my vise grip.  twist the gun and off it goes.