What is Headspace?
Simply put, headspace is the distance from the breech face to that part of the chamber which stops forward movement of the cartridge case. Insufficient headspace interferes with closing the gun because it leaves insufficient room for the cartridge. Excessive headspace permits the cartridge case to be unduly stretched or even separated by the gas pressure in firing. Both of these cases are dangerous due the possibility of serious injury during firing, if the gun will fire at all.
