Few topics inspire as much interest and confusion as headspace.
It is one of the few technical small arms terms recognized, if not understood, by even beginning shooters. It is seldom firmly understood by even experienced shooters. In a narrow sense, headspace is the size of the cartridge chamber designed to accept a particular cartridge. Headspace is defined as minimum and maximum dimensions from the locked breech to either a contact surface or designated datum in the rifle chamber, or to the rear of the barrel. In a broader sense, headspace is a far more complex relationship between the cartridge, chamber, and firearm mechanism.