One thing I do not remember being addressed, when backing the sizing die out to partal resize, is squaring the sizer with the shell holder. All instructions I have say to raise the ram to full height, then screw die down to contact shell holder and then tighten lock ring.
One of my reloading books said this has a two fold purpose. One to bring brass shoulder to correct spec and two, to square the sizing die with the shell holder. This makes sense because the 7/8-14 threads have a lot of slack.
Depending on how far I want to back the sizer off I use a feeler gauge between the die and shell holder to get them squared. Most of the time I use a .035 gauge that equals about 3/4 turn of the die. Unless there is hole in the gauge don't forget to remove the decapper first
Ken