Bolt Face
The recessed front surface of the bolt that supports the case head during firing, sized to match a particular family of cartridge rims.
The bolt face is the flat, recessed front of the bolt that the case head seats against when a round is chambered. It contains the rim and base, supports the brass against the rearward thrust of firing, and houses the firing pin hole at its center along with the cuts for the extractor and ejector.
Bolt faces are machined to standard diameters that correspond to cartridge-rim families, such as the common .473 inch face shared by the .308 and .30-06 head sizes, or the larger magnum and rebated-rim dimensions. The extractor rides in a slot on the face to grip the rim, and the depth of the recess factors into the rifle’s headspace, so a barrel and bolt must be matched to the same cartridge family.