Hang fire refers to an unexpected delay between the triggering of a firearm and the ignition of the propellant. This failure was common in firearm actions that relied on open primer pans, due to the poor or inconsistent quality of the powder. Modern firearms are susceptible also.

Why do we say hang fire?

It dates from a time when firearms were loaded using a gunpowder charge poured from a flask, which was then ignited by a spark from a flint striking against an iron plate. ... When this happened, the powder in the firearm smouldered instead of exploding and was said to hang fire.

What does the expression mean hang fire?

Delay, as in The advertising campaign is hanging fire until they decide how much to spend on it. This expression originally referred to the 17th-century flintlock musket, where the priming powder ignited but often failed to explode the main charge, a result called hanging fire. [