Hang fire

Revolver that has suffered from a hang fire
USS Nicholas (DD-449) suffered a hang-fire 127 mm (5 inch/ 38 caliber) gun mount on 13 May 1943, resulting in the gun exploding with no casualties

Hang fire is an unexpected delay between the triggering of a firearm and the ignition of the propellant.[1] This failure was common in firearm actions that relied on open primer pans, due to the poor or inconsistent quality of the powder, although modern firearms are also susceptible. The delay is usually too brief to be noticed, but can be several seconds. A hangfire should be suspected whenever a firearm fails to fire, but has not clearly malfunctioned.