But if you size with a bushing spring back reduces neck tension.
If you size with a mandrel or expander ball spring back raises neck tension
As the brass work hardens this effect is more pronounced. Annealing every firing makes the spring back effect consistent instead of changing with every reloading cycle.
I get your point now. I need to do some measurements after bushing sizing. For small dimension changes the spring back may be negible. Need to check this out and get some real numbers. True tension/grip is more complicated than just the neck diameter change after inserting a bullet. Actual hardness and dimension change. My Redding FL non bushing die closes the necks down way to much. The bullet expands the neck about 6 thou. You can control the diameter change better with a bushing die or a custom die made to match fired cases. I agree now with your comment.