Forster Headspace Go 303 British

Choosing the Correct Gage According to SAAMI (Sporting Arms and Ammunition Manufacturers Institute), who set product standards for firearms and ammunition, headspace is “The distance from the face of the closed breech of a firearm to the surface in the chamber on which the cartridge case seats. Some shooters are under the misconception that headspace is fixed over the life of the firearm. Headspace can increase after repeated use of ammunition that causes too much pressure. Handloaders should routinely check rifle chamber headspace every thousand rounds.

Headspace is measured differently depending on whether the firearm’s caliber uses rimmed, belted or rimless cartridges.