Recovery/memory, then there is 'spring back', I am not a fan of spring back, there are many things that can not be done because of spring back, I have crushed cases with a hammer, not one of the cases crushed displayed spring back, I have dented cases with a punch and hammer again none displayed spring back. I have formed 30/06 and 280 Remington cases to everything from 257 Roberts to 35 Whelen, in all of those cases I have never had one spring back, none ever recovered and not one of them had a memory of ever being a 30/06 or 280 Remington.
Measuring the inside diameter of the neck after sizing requires a different tool then the dial caliper, if it is important I will use a hole gage/wire gage. New (annealed) brass is malleable and has what was once called bullet hold, now it is called bullet tension, the diameter of your sizer ball should not be 308 if the bullet diameter is .308, the sizer ball can be ordered in different diameters, some grind, file, sand etc., the sizer down but that does not seems to be the problem, seems the mouth of the case needs a bevel on the inside and or the flat base of the bullet is square.
Not practical: I made a tool for seating bullets in 25 cal cases, it sits on the shoulder and is larger in diameter than the outside of the case neck until the bullet is seated, then it fits, the hole in the top is .250 in diameter, the bottom of the tool centers the neck, the hole in the top centers the bullet, the bullet can not get off center, canted or crooked, the bottom of the tool sits on the shoulder, I set the case, bullet and tool upright on an aluminum can crusher and pulled the handle, it worked. The RCBS competition/precision seater die works in a similar manner except there guide is pushed up inside the die by the case and the bullet is held up by the case mouth until seated. This design greatly reduces the chance of something going wrong after the pullet is released when seating, Hornady uses a bullet guide in their New Dimension seater dies.
Bullet hold is determined by the condition of the brass in the neck neck and difference between the inside diameter of the neck and outside diameter of the bullet, meaning the hole in the neck is smaller than the bullet, when the bullet is seated, the neck stretches, measure the outside diameter of the neck before seating the bullet, measure again after seating the bullet, the difference determines the amount of case stretch, again if the hole is .308 and the bullet is .308 there is no bullet hold/neck tension or stretch.
Stretch/flow and spring back, or memory / recovery, then there is 'it can not be done because of spring back'.
F. Guffey