Headspace
Definition
The dimensional distance from the bolt face to the datum line in the chamber at which the cartridge case head rests; excessive headspace produces case stretching visible as a bright annular ring on the fired case body.
- Definition
- Bolt face to chamber datum-line distance
- Measured at
- Point cartridge case head rests
- Excess effect
- Case stretching
- Visible sign
- Bright annular ring on fired case body
Common questions
Why does excessive headspace matter for cartridge case identification?+
Excess headspace lets the case stretch and thin near its head before the primer seats fully against the bolt face, which alters the depth and clarity of firing pin and breech face impressions and can complicate matching a case to a firearm.
Is the bright annular ring from excessive headspace unique to a particular class of firearm?+
No, it can occur in any firearm with worn or out-of-specification chamber dimensions, so the ring indicates a headspace problem in that specific gun-ammunition combination rather than identifying a firearm type or manufacturer.
Related terms
- Ball Propellant
- Spherical or slightly flattened-sphere propellant grain used in pistol and some rifle cartridges; meters consistently through powder dispensers and produces a specific...
- Belted Case
- Cartridge case with a raised band (belt) ahead of the extractor groove that controls headspace; found in large-calibre magnum cartridges including .300...
- Berdan Primer Pocket
- Primer pocket with an integral anvil post and two offset flash holes; the primer cup has no anvil. Standard in European commercial...
- Boxer Primer Pocket
- Primer pocket with a single central flash hole; the primer anvil is integral to the primer cup. Standard in US commercial production....
- CIP
- Commission Internationale Permanente pour l'Epreuve des Armes a Feu Portatives; the European proof body that standardises chamber and cartridge specifications for European...
- Extruded (Stick) Propellant
- Cylindrical rod-shaped propellant grain with single or multiple perforation; dominant in medium- and slow-burning rifle propellants for 5.56mm, 7.62mm NATO, and larger...
- Gilding Metal
- 90 percent copper and 10 percent zinc alloy used for bullet jackets in most commercial FMJ and jacketed pistol ammunition; softer than...
- Obturation
- The gas-sealing function of the cartridge case during firing, in which the case wall expands outward under propellant pressure to seal the...
- Rimless Case
- Cartridge case geometry where the extractor groove is machined into the head and the rim diameter equals the body diameter; dominant in...
- SAAMI
- Sporting Arms and Ammunition Manufacturers' Institute; the US voluntary standards body that publishes chamber and cartridge drawings and maximum average pressure (MAP)...
- Slamfire
- Unintended cartridge ignition during bolt closure, without a discrete trigger pull. Caused by free-floating firing pin inertia or primer over-sensitivity. Produces automatic-like...
- Squib
- A cartridge where primer fires but propellant combustion is partial or absent, leaving the projectile lodged in the barrel; the case shows...