What is a "Misfire" in Shooting?

Traditions Colt Single Action Army 45 Revolver - Firing Pin and Hammer Disassembled
This revolver required some repair work when it began misfiring. Photo © Russ Chastain

Definition

The term misfire refers to the situation in which a gun fails to fire when the shooter pulls the trigger. It is the complete absence of ignition of the primer and powder in the ammunition round. 

Misfires are by far most common with muzzleloading guns (most often with flintlocks), but they do also occur in cartridge-firing guns. Should a misfire occur, shooters are well advised to keep the gun pointed in a safe direction for several seconds after the gun fails to fire, being prepared for a hangfire--the situation where the firing is delayed.

If the gun fails to fire completely after 30 seconds or more, the shooter should unload it carefully before proceeding.

Once the dud round is cleared from the chamber, you should safely dispose of it, as it is not safe to reuse. 

Causes of a Misfire

Misfires may occur because of mechanical problems in the gun itself, or due to problems with the ammunition round--specifically with the primer or powder. 

Causes of misfires are many and varied. In examining a misfire, the first thing to assess is whether the gun performed its mechanical function properly. Did the firing pin strike the primer (or the rim, on rimfire ammunition) firmly and in the proper position? In many cases, it may be a mechanical problem with the firing mechanism that causes the misfire. But If the firing pin struck the primer or rim properly and firmly, then the ammunition is probably at fault. How do you know if the firing mechanism was operating correctly?

You will normally see the mark from the firing pin on the head of the shell casing when you remove the misfired cartridge from the chamber of your gun.

A gun that frequently misfires should probably be serviced, with attention paid to the firing pin and trigger mechanism. 

If not a mechanical problem, then a misfire is likely due to an issue is with the ammunition round itself.

In muzzleloading arms, take a look at whether the percussion cap, musket cap, or the powder in the pan has properly ignited. If so, try again with a new cap or FFFFg powder. If the gun still fails to fire, the main powder charge may be fouled, and pulling the bullet may be the best way to unload the gun.

Cartridge ammunition may misfire because of a bad primer or a bad powder charge within the cartridge. You may see this when ammunition is very old or if it has been stored in a damp location. A box of ammunition that has one bad round may well have others.