So you've just aimed at the target and pulled the trigger of your firearm and the hammer falls on the cartridge and then, nothing happens. You may have just experienced either a hang fire, or a dud cartridge. What is going on here?
First, let us examine the phenomenon known as "hang fire" (also known as "delayed discharge"). This is when the trigger is pulled and the hammer releases properly, but there is a perceptible delay between when the hammer is released and when the firearm shoots. The delay time can vary: it can be only a fraction of a second to many seconds later. This may have the effect of throwing off the shooter's sense of timing and cause him/her to miss the target. In the case of propeller driven aircraft from World War I and World War II, the result was sometimes more catastrophic. You see, in those days, fighter aircraft used to have an interrupter gear (a mechanism invented by a Dutch man, Antoine Fokker during World War I) that allowed the aircraft to shoot its guns through a rotating propeller. The mechanism ensured that the aircraft's guns would only fire when the propeller blade was not in front of them. However, with hang fire happening, this could cause the bullets to come out a fraction of a second too late and strike the rotating propeller blade.
In the early days of firearms such as matchlocks and flintlocks, this is how all firearms worked -- there was always a delay from pulling the trigger to when the firearm discharged. In fact, the inventor of the percussion lock specifically designed his firearm to solve this delay issue. However, the issue was not completely solved and still happened because the quality of the powder wasn't always good quality in those days. It is still a problem in modern times too, because even if the production methods and quality of powder have improved, it may still happen if someone stores the ammunition improperly, or if the ammunition is too old. Ammunition which has been stored in damp conditions or exposed to penetrating cleaning solvents such as WD-40 may experience hang fires or become dud cartridges. Reloaded cartridges may also experience this issue if they haven't been cleaned properly prior to reloading (for example, the primer pocket in the cartridge may be partially blocked with residue). Finally, factory manufactured cartridges may also have this issue if they are very old or if they have been manufactured using improper methods and bad quality control.
When a hang fire occurs, the primer goes off, but the main propellant in the cartridge doesn't burn right away and it burns slowly until it builds up enough pressure to push the bullet out of the crimp of the cartridge and out of the barrel. This may take a few seconds to accomplish.
A dud cartridge will not fire at all. The reasons for this happening are similar to that for hang fire (i.e.) bad ammunition or incorrect storage of the ammunition. Other reasons that could cause dud cartridges include putting in a bad primer cap or forgetting to load propellant in the cartridge.
So what should a user do after they have pulled the trigger and nothing happens? Is this because of a dud cartridge or is it hang fire and how can the user tell the difference?
The user should continue to point the firearm in a safe direction for about 30 seconds, just in case it is a hang fire. If the firearm doesn't shoot after 30 seconds, the user may then conclude that the cartridge is a dud and remove it from the firearm. It is not a good idea to start examining the firearm right after it fails to fire because it may just be delayed due to hang fire.
The video below is an example of what NOT to do:
The user is the above video is very lucky to be alive. After his gun failed to fire, he immediately decided to look down the barrel to see what was wrong, instead of waiting for 30 seconds in case it was a hang fire. He was very lucky that the bullet didn't hit him when the gun finally fired.
If the firearm hasn't fired after 30 seconds, then it may be concluded that this is not a hang fire and that the cartridge is a dud. The cartridge may then be removed, but it should be disposed off safely. Why? Because there is a dangerous possibility that the cartridge can fire later on (for example, it may not have fired because the primer cap was bad, but the propellant inside the cartridge is still good and can go off if exposed to flame or heat).
Some ammunition factories have very poor quality control and manufacturing methods, and their ammunition is sold especially cheap. For example, .303 cartridges manufactured by POF (Pakistan Ordinance Factory) have a reputation for being of very poor quality and experiencing several hang fires and dud cartridges in every box of ammunition and several Enfield users recommend not buying them from this manufacturer at all. The video below shows one user's experience with 20 cartridges made by POF:
As you can see from the video, of the 20 cartridges fired, 8 were duds and didn't shoot at all and many of the remaining experienced hang fire, which can clearly be seen in the video when the user shoots. The user does not save any money by purchasing such cheap low quality ammunition, as it is unreliable and quite dangerous to shoot with.