I would advise any ngrs owner to have an AR wrench. The recoil/wobble causes stuff to get loose surprisingly fast. They can generally tighten the barrel nut as well (which on recoils needs doing occasionally).
For the castle nut, it's needs tightening but I'd also recommend some threadlock (can't remember if it's blue or red).
I'd also recommend checking other screws and pins periodically as well, at least after every game day for the first 3-5 game days you do, mag catch, the ones in the stock tube, the pins in the lower receiver. Just a standard side effect of the recoil.