Originally Posted by Mikecr
Biggest contributors to bad seating: threaded die/press seating(instead of inline/arbor), and seating force variance/excess seating forces.
True story. Noticed years ago when seating sets of bullets with different powder charges. When the powder started getting crunched, the OAL would lengthen, even with no change to the seating die. Also a smaller ID will lengthen OAL as I'm sure variance in brass elasticity from annealing will change seating depths unless adjusted for.
Comparators are typically (at least all I have measured) .011" below caliber
Here a .308 comparator
and the seating stem (taken from unused RCBS FL seater and measured as close as I could to the first surface to hit bullet) is ~.260"