Like the snaplock and the snaphaunce, this weapon has a serpentine hammer, which has jaws at the end, to which can be screwed on a piece of flint. Like the other two weapons, it has a steel (called a "frizzen") facing the piece of flint. When the trigger is pulled, the flint strikes the steel and releases sparks. Here's where the flintlock's innovation comes in. The steel frizzen is shaped like the letter 'L'. The horizontal part of the 'L' covers the firing pan where the priming gunpowder is. So the flint on the falling hammer strikes the frizzen and causes sparks of hot steel to form. As it is falling, it also pushes the frizzen away from the flint, thereby opening the pan cover and exposing the pan's contents. So the generated sparks will fall into the pan and light the priming powder that is in the pan.
If all goes well, the priming gunpowder in the pan will light. There is a tiny hole in the pan that leads to the main charge of gunpowder in the barrel. The flame will travel through this tiny hole and light the main charge and the weapon discharges. If all doesn't go well, the sparks may not fall into the pan, or the powder in the pan may light, but doesn't light the main charge. This is called a "flash in the pan", i.e. a flashy initial start, but no results.
The advantages of this weapon over its predecessors are many:
- Unlike the matchlock, this weapon doesn't require the user to carry an lit match at all times to discharge the weapon. Hence it is much safer to use, especially in larger groups of soldiers or near gunpowder supplies. It can also be used more reliably in rainy weather.
- The mechanism is not as expensive to manufacture as the wheel-lock and doesn't require as much specialized metallurgical and mechanical knowledge to manufacture.
- Unlike the snaplock, the cover for the pan opens automatically when the trigger is pulled. Hence it is possible to carry the firearm loaded in damp conditions and not worry about the gunpowder getting wet, as the pan cover opens right as the sparks are generated.
- Unlike the snaphaunce, there are fewer parts in this firing mechanism, as the pan cover and the steel are the same part. Hence, this leads to better reliability and less cost.
While the half-cock position was supposed to be "safe", sometimes a faulty safety mechanism would release the hammer from this position and it would strike the frizzen. Striking the frizzen from the half-cock position wasn't supposed to have enough force to cause sparks to form, but occasionally this would happen and the weapon would discharge. This is the origin of the modern-day phrase "going off half-cocked", which means "to take a premature action".
Flintlocks stayed with us for a very long time. The mechanism was invented in the 1600s and was used till at least 1850 or so. Some flintlock weapons are manufactured even in this present day, for hunting enthusiasts who prefer to use black-powder weapons.