From Texas10.....Case length (neck length) differences will indeed affect neck tension. How well are you holding case length from base to shoulder (datum) and how much are you setting back the shoulder when you FL size? Or are you neck sizing only the twice fired brass?
Texas10 is right on the money with neck tension variation. Using a screw in die some times a tight neck will not fully seat a bullet with a consistent stroke of the press. If you want the consistent seating depth, try using an expander mandrel (like a a k&m) not the one in your sizing die along with an arbor press and a Wilson seater. You will see a noticeable difference.
Darrin[/QUOTE]
I’m FL sizing with honed neck from Forster (without the expander button) then expanding with a Sinclair mandrel .002” smaller than bullet diameter...