Totally agree on most of it being the gun.
If I recall a few years ago, few reasons for settling on current process based off nothing more than researching well known guys processes on YouTube and forums;
Pulling decap/expander ball out of FL die, and adding mandrel step (which then adds the moly step to lube mandrel) was to better control neck tension/interference with interchangeable mandrels (I use "turning arbor" .002 under) Also pulling expander ball up could pull out headspace, more so than pushing mandrel down.
Going with die wax on case body only, over oneshot, was intended to prevent oneshot from getting into necks, be it at all, or even inconsistently (only on one side of neck, or some in one case, none in another). Somewhat tied into getting moly in there for the mandrel. Allows consistant neck condition for expansion/sizing, as well as bullet seating and bullet release.
While this process has worked well for me on multiple rifles, want to make it clear that I am not a firm beleiver in the reasons above, and would gladly see them to be proven wrong. Just seamed like the best way to go about it at the time, and kinda just settled in to what worked. Food for thought in further testing.