Squib
Definition
A cartridge where primer fires but propellant combustion is partial or absent, leaving the projectile lodged in the barrel; the case shows a normal primer strike but minimal case expansion; a diagnostic failure mode in misfire investigations.
- Cause
- Partial or absent propellant combustion
- Primer status
- Fires normally
- Projectile outcome
- Lodged in the barrel
- Case indicator
- Minimal case expansion despite normal primer strike
Common questions
How does a squib differ from a simple misfire?+
A misfire is a complete failure to fire, usually from a primer or ignition fault, while a squib does fire but with insufficient propellant burn, so the case shows a normal primer strike yet the bullet never fully exits the barrel.
Why is recognising a squib important during a shooting reconstruction?+
A squib leaves an obstruction in the bore that, if unnoticed, can cause a catastrophic barrel failure on the next shot, so examiners look for it when a recovered firearm or scene evidence suggests an interrupted firing sequence.
Related terms
- Ball Propellant
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- Belted Case
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- 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...
- Headspace
- The dimensional distance from the bolt face to the datum line in the chamber at which the cartridge case head rests; excessive...
- 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...