The reason I suggested NK sizing a couple of times is to be sure that the case shoulder will get pushed forward to where chambering has some level of resistance. At that point, you can be sure that the case shoulder has reached the max point and is ready to be bumped back the desired amount.
If the case shoulder does not reach that resistance point, how will we know how much of a shoulder bump is required. Mr Guffy would measure and would know the desired case length and how much adjustment to the shoulder is needed, but I don't have the measuring equipment and don't see the need to spend the money if I don't have to.
As to whether a fellow should NK size or FL size depends on a few factors. If you load max loads, just go ahead and FL size. If you shoot light loads, you can probably NK size quite a few times before the shoulder needs to be bumped back, if you wish. And, regarding accuracy, try the respective dies and see what shoots best. Depends on your rifle, the chamber and the dies themselves. You may not see much difference with ammo from the two die types.
