Forster Rimmed and Belted Headspace Gage, GO length, for 30, 40 Krag, BG3040G

"Forster Rimmed and Belted Headspace Gage, GO length, for 30, 40 Krag, BG3040G. Headspace is the distance between the face of the breech and the base of the cartridge when the action is closed and excessive headspace can be dangerous as well as impair accuracy.