RE: Neck sizing w/ Full length die????
Yes you can ! It takes some adjusting of the die and the decapper !
If you have Hornady dies or Lee,it is a pain in the neck,to adjust them ,because of the pinch nut that holds the decapper pin .
On others,un-screw the decapper,up to where it is away from knocking out the primer. Next,adjust the die body down to the amount you wish to size the case neck ? I use to use graphite on the neck,as a way to see just how far down I had come.Then,once set up,re-adjust the decapper pin,to knock out the primer .