If that's done with a regular full length sizing die, the case body is also sized down. Mic the body diameters before and afterwards to see the difference.To neck size, I lube the neck with say Imperial Wax. Then I start to screw down the resizing die and watch the lube rubbed off until I get to the base of the neck where it meets the shoulder. The theory behind it is that the case has been expanded to your chamber and is the best fit for your rifle now.
Yes.when the ram is fully raised the entire body of the case is fully supported by the walls of the die . The neck and body are being squeezed by the walls of the die and in effect it is being cold extruded. When the ram is being lowered the point where the expander ball is dragged back through the neck the body is not supported. Misalignment of the body and neck can only occur at the time the case body is free floating inside the die