HEADSPACE is a ballistic term which crops up frequently in print. Too bad it is seldom accurately defined, because its effect on the cartridges you load, and the adjustment of the dies, is critical. If you want to be a truly safe and effective handloader, the concept and practice of headspace must be understood and adhered to.
An important mechanical aspect of a cartridge case is its system of headspacing, which is a dimension within the rifle’s chamber. Specifically, it is the distance between the bolt face and a datum point within the chamber, but it may also be defined as the amount of forward and backward movement of a chambered cartridge when the breech is closed and locked.
Ideally, this endplay should be zero, but this is impractical in factory ammunition because of manufacturing tolerances in both cartridges and chambers. Therefore, industry standards set allowable headspace at .004” (0.1mm) maximum. Four one-thousandths of an inch is not a great deal of space, but more headspace than this in a chambered cartridge is considered excessive and potentially dangerous.
There are four common methods of determining
