Originally Posted by jimbires
yes you should be resizing the whole neck , with the die adjusted this way . some guys still neck size only , I don't . I do have a few Lee collet dies , these only neck size , but then I also use a body die to push the shoulder back 0.002 . which is basically doing the same thing as using a full length die.
In measuring neck runout on resized cases using neck only as well as full length dies (both with die neck diameters .002" smaller than a loaded round's neck), the full length ones better center the neck on the case shoulder. The body's held well in place as the neck's sized all the way down setting the shoulder back a bit.
If the case neck's not centered on the shoulder on a case headspacing on its shoulder, both the neck and bullet will not be centered in the chamber throat.
I believe all of this is why most benchresters finally switched over to minimal full length sizing their fired cases.