The main causes of misfires are:
- Priming inert: the firing cap of a cartridge or caplock, the powder priming of an older lock type (e.g. a flintlock) or the detonator of an explosive charge has failed to function, either because it proved to be inert, has become damaged (e.g. wet priming powder) or dislodged or was not powerful enough for the task.
- Charge inert: the propellant (in a firearm) or the explosive (otherwise) is not of sufficient quality and/or quantity to detonate.
- Firing malfunction: the firing system, whether firing pin, lock or detonator trigger has malfunctioned and is not sending a correct signal - a firing pin may be bent, a wheelock worn so that it doesn't spark and a detonator trigger failing to generate enough current.
Typically the operator must first ensure that the system has misfired1. The next step then depends on his system - for a repeating breech loader the most sensible response is to cycle the action, eject the misfired round and chamber another. For explosives and muzzle loaders most schools of thought recommend re-priming and trying again.
If a breech loader fails to fire after cycling the user's next response will depend on the characteristics of his weapon - often he will try a different source of ammunition to ensure that he hasn't received several bad rounds and/or examine the extracted rounds to see if they are being struck. Failure to strike, or any other inability to fire ammunition known to be good will tend to imply the misfire was a type 3 and the weapon needs to be taken to a gunsmith. If cycling new ammunition in solves the problem the misfire was likely to be type 2 or 1.
For explosives and muzzle loaders, re-priming should solve a type 1 misfire, if that fails the next step is to check the firing mechanism for faults in hope of detecting a type 3. Type 2 misfires require the replacement of the whole charge, which is typically laborious and sometimes dangerous as well.
"Squibs" where the propellant fires with reduced force or "bombs" where it fires with more force than expected are also misfires, and are typically far more dangerous - a round that bombs can damage or even burst the weapon, whilst a squib can, in extremis, leave a round stuck in the barrel for the next shot to hit. Both of these can be caused by poor quality control during manufacture of either the whole cartridges or just the propellant or by aging or contamination of stored ammunition. Home made ammuntion produced by inexperienced handloaders is especially prone to these sorts of misfires2. Likewise, improvised, elderly or mistreated explosives also have a tendency to misbehave.
Game and Story Use
- In the modern era, a misfire is trivial as long as the user doesn't panic and/or mistake it for an empty weapon. In previous eras it can render the firearm useless for hours. Amateur users may need to make appropriate self control checks if their weapon suddenly fails in the heat of battle.
- "Try looking down the barrel and see if something's stuck!" (makes secret smarts roll…)
- The misfired demolition has, historically, been the source of much hilarity - going back to a partially fired charge is never all that safe, and to do so in a hurry, possibly under enemy fire, even less so - nonetheless, a good few combat engineers have been highly decorated for reviving a failed demolition on a key gate or bridge whilst under fire.
- A hang fire traditionally waits until the user is no longer holding his weapon properly (or is on his way to check the detonators) before going off.