When you start an FL resize cycke, as soon as the sides of the die touch the sides of the case, they start squeezing it out longer than it started. Encountering the shoulder in the die then pushes it back again. The wild card is usually the expander. It can sometimes pull a shoulder forward again if there isn't enough inside neck lubrication (or sometimes even if there is). If you haven't tried it yet, remove the expander from your FL die and see what you get after the resizing. The necks will be too narrow, but you can widen them by putting the expander back in, lubing the necks inside, then running them up over the expander. Then see what you have afterward and how it compares.
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