Obturation
Definition
The gas-sealing function of the cartridge case during firing, in which the case wall expands outward under propellant pressure to seal the chamber and prevent rearward escape of combustion gas past the case body.
- Core Function
- Gas-sealing between cartridge case and chamber wall during firing
- Primary Cause of Failure
- Oversized or poorly manufactured chambers in firearms
- Visible Signs
- Bulged or split cartridge cases, reduced bullet velocity
Common questions
What happens if obturation fails in a firearm?+
Poor obturation allows combustion gases to escape around the cartridge case instead of staying contained. This causes the bullet to leave the barrel at lower velocity and the cartridge case itself may bulge or split from uneven pressure.
Why do country-made firearms often have obturation problems?+
Country-made guns typically have oversized or poorly manufactured chambers that don't fit standard cartridge cases snugly. This prevents the case wall from expanding fully to seal against the chamber, leading to partial obturation and gas leakage.
How does obturation affect bullet performance?+
Good obturation keeps combustion pressure high and contained, which accelerates the bullet consistently down the barrel. When obturation is poor, gas escapes early, reducing the propellant pressure that pushes the bullet forward and lowering its muzzle velocity.
Related terms
- Arms Act 1959
- Principal Indian statute regulating manufacture, possession, transport and sale of firearms and ammunition. Possession of an unlicensed country-made firearm is punishable under...
- 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...
- Country-Made Firearm
- An illicitly manufactured firearm, fabricated in unlicensed cottage workshops without quality control, typically smoothbore and chambered loosely. Generic Indian umbrella for katta,...
- 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...
- Headspace
- The dimensional distance from the bolt face to the datum line in the chamber at which the cartridge case head rests; excessive...
- Katta
- Single-shot crude pistol, usually.315 or 12 bore, with a break-action or screw-plug breech and a nail-head striking pin. Dominant illicit firearm in...
- Mikrosil Casting
- Two-part silicone casting compound used to make a negative replica of a chamber, breech face or tool-mark. Standard at Indian CFSL ballistics...
Explained in these topics
- Cartridge Anatomy: Case, Primer, Propellant, ProjectileThe gas-sealing function of the cartridge case during firing, in which the case wall expands outward under propellant pressure to seal the chamber and prevent...
- Examination of Country-Made Firearms (Kattas and Tamanchas)The seal a cartridge case makes against the chamber wall on firing. Oversized chambers in country-made guns give partial obturation, leading to gas escape, low...