Wheellock
Wheellock, also referred to as 'Wheel-Lock', is a method for igniting the propellant of a loaded gun's bullet. It was the first self-igniting firearm. Developed around the 1500s it replaced the matchlock and was superceded by the snaphance (1580s) and the flintlock (around 1600).On pulling the trigger a metal spring unwound and through an axle and chain spun a serrated steel wheel against a material like iron pyrites held in a cock. This generated sparks which fell into the priming pan, igniting the powder there and so ignited the main charge. Each firing of the gun required the main spring to be rewound, using a special lever and called 'spanning the lock'. The sparking material would last around a dozen shots before needing replacing. A single shot took around a minute to load, prepare and fire.
The invention is usually credited to Johann Kiefuss in 1517 in Germany. That he was actually the inventor is unlikely, writings refer to weapons that are clearly not matchlocks in the previous decade. However, his is the first name to be linked to the gun.
The advantage over the matchlock was a comparatively much better resistance to rain or damp -- sparks could be generated in any weather and the priming pan was fitted with a cover that was not raised until the instant of firing. The high production cost hindered its widespread adoption. Construction required a skilled gunsmith, the mechanism was complex and so more likely to break. Early designs had trouble with reliable springs, though these problems were solved in time. It was used along side the matchlock until both were replaced by the faster, simpler and less costly flintlock of the 1600s. However, the better firing of the wheellock in the wet meant that well-made guns of this design were used until the 18th century.