Headspace - What is it?
In the case of rimmed 7.62x54R ammunition, the ideal headspace is equal to very slightly more than the thickness of the cartridge rim. Too little
headspace will prevent the bolt from closing completely (or not at all) on
a cartridge. Too much headspace can result in a gap between the bolt face and the base of the cartridge (or a gap between the rim and chamber) that can cause a devastating release of high pressure gas into the receiver when a round is fired. The sudden release of this gas into an area of the firearm not designed to contain it can cause serious injury or death to the shooter and bystanders as the receiver disintegrates, and is not something to be taken lightly.
