Neck Sizing
Sizing only the case neck while leaving the fireformed body untouched, so the case keeps a tight custom fit to one specific chamber.
Neck sizing resizes just the neck of a fired case to grip a new bullet, deliberately leaving the body and shoulder in the shape the chamber formed them. Because the body is not pushed back down, the brass stays matched to that one rifle, which some shooters credit with better alignment and longer case life. It also works the metal less than running the whole case through a die.
The tradeoff is fit: a neck-sized case is sized to one chamber and may chamber stiffly or not at all in another rifle. Specialized reloading dies handle the neck alone and still let you set a precise neck tension on the bullet. After several firings the body eventually grows enough that a full-length sizing pass is needed to restore reliable chambering.