Shoulder Bump
Setting the case shoulder back a few thousandths during sizing to control headspace and let the bolt close cleanly on the chambered round.
Shoulder bump is the small, deliberate setback of the case shoulder when a fired case is resized, measured in thousandths of an inch from its fireformed position. Firing pushes the shoulder forward to fill the chamber, and bumping it back the right amount restores the headspace fit so the round chambers without forcing the bolt. Too little bump leaves a stiff close, while too much overworks the brass and can shorten case life.
Most precision loaders aim to bump the shoulder only a couple thousandths below the rifle’s actual chamber, measured with a comparator rather than guessed. This is set by how far the case is screwed into the full-length die, so careful adjustment of the reloading dies is what makes the bump consistent. The goal is a round that drops in and the bolt closes on with light, even resistance.