Slamfire
Definition
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 fire from a semi-automatic weapon; must be distinguished from intentional auto-sear modification.
- Trigger involvement
- Occurs before any deliberate trigger pull.
- Weapon state
- Happens during the chambering stroke, before the bolt fully closes.
- Root causes
- Free-floating firing pin inertia or primer over-sensitivity.
Common questions
What exactly happens when a gun slamfires?+
The weapon fires unexpectedly as the bolt chambers a round, before the shooter pulls the trigger. The firing pin strikes the primer either due to inertia or sensitivity issues. From a semi-automatic gun, this produces full-auto-style bursts.
How do forensic examiners know a slamfire happened instead of intentional fire?+
The cartridge case shows a firing-pin indent that is often offset or preceded by multiple marks from the chambering stroke. These marks reveal the firing pin struck at the wrong moment in the cycle. Slamfire must be distinguished from intentional auto-sear modification, which has a different mechanical origin.
What causes a gun to slamfire?+
The firing pin may float loosely instead of being properly fixed, so impact during bolt closure ignites the primer. Or the primer itself may be too sensitive. Either way it is a mechanical failure, not a shooter error or design intent.
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....
- Chamber Pressure
- The gas pressure inside the firearm's chamber and bore during combustion of the propellant charge. Measured by piezoelectric transducer in psi (SAAMI)...
- 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...
- Hangfire
- A delay between firing-pin strike and cartridge ignition, ranging from fractions of a second to several seconds. Caused by degraded or moisture-contaminated...
- Headspace
- The dimensional distance from the bolt face to the datum line in the chamber at which the cartridge case head rests; excessive...
- Maximum Average Pressure (MAP)
- The SAAMI statistical ceiling for mean chamber pressure across a production lot of cartridges, at specified temperature and barrel conditions. CIP uses...
- Obturation
- The gas-sealing function of the cartridge case during firing, in which the case wall expands outward under propellant pressure to seal the...
Explained in these topics
- Cartridge Anatomy: Case, Primer, Propellant, ProjectileUnintended weapon discharge during the chambering stroke before deliberate trigger pull; case shows a firing-pin indent that is often offset or preceded by mul...
- Ignition, Combustion and Chamber-Pressure CurvesUnintended cartridge ignition during bolt closure, without a discrete trigger pull. Caused by free-floating firing pin inertia or primer over-sensitivity. Prod...