Freebore
The unrifled length of bore just ahead of the case mouth that a bullet travels before the rifling engages, setting jump and usable cartridge length.
Freebore is the cylindrical, unrifled portion of the throat that a bullet must travel after leaving the case mouth and before the rifling starts to grip it. It is measured as a length, and the amount a chamber carries is a deliberate design choice that influences both pressure and accuracy tuning.
More freebore lets a bullet be seated farther out without touching the rifling, which raises usable cartridge length and powder room inside the chamber, while also lengthening the bullet jump to the lands. Shooters balance that jump against pressure and seating room when they set seating depth, so freebore is a number that handloaders pay close attention to in any precision chamber.