Rmeju, first, the case has a case length, head space is not a case thing, the case has a length from the shoulder/datum to the head of the case, that is the reason L.E. Wilson labels their case gage as case length gages, others refer to their gages as head space gages.
The chamber has head space, head space is measured from the shoulder/datum to the bolt face, head space, to me, is a blank that is to be filled in as is , after I fill in the blank I use the diminution to measure cases before firing, after after firing and again after sizing. I have more confident in my equipment than most reloaders, I adjust my die to and or off the shell holder with a feeler gage.
Back to neck sizing, 918V is correct, neck sizing is neck sizing, there are no shades and or excuses, anything beyond neck sizing is sizing, and as 918V said, there is no way to neck size with a full length sizer if the die contacts the shoulder after the die contacts the case body, there are degrees of sizing, anything less than knowing the length of the chamber from the shoulder to the head of the case is just going through the motion, again, I adjust the die to avoid sizing the case more than necessary, without filling in the blank after head space a reloader is talking about reloading, sizing, neck sizing, and bumping. I can not bump, again, when the sizer die bumps? the shoulder the same die has already contacted the case body and case shoulder etc., again, I control the length of the case with the threads provided on my press and die, and because installing a micrometer is not convent I use the feeler gage.
http://www.saami.org/PubResources/CC_Drawings/Rifle/7mm Remington Magnum.pdf
Notice the link furnished head space diminutions on the chamber, not the case.
F. Guffey