Wheel lock

A wheellock, wheel-lock or wheel lock, is a friction-wheel mechanism to cause a spark for firing a firearm. It was the next major development in firearms technology after the matchlock and the first self-igniting firearm. Its name is from its rotating steel wheel to provide ignition. Developed around 1500, it was used alongside the matchlock and was later superseded by the snaplock (1540s), the snaphance (1560s) and the flintlock (c. 1600).

The wheellock works by spinning a spring-loaded steel wheel against a piece of pyrite to generate intense sparks, which ignite gunpowder in a pan, which flashes through a small touchhole to ignite the main charge in the firearm's barrel. The pyrite is clamped in vise jaws on a spring-loaded arm (or 'dog'), which rests on the pan cover. When the trigger is pulled, the pan cover is opened, and the wheel is rotated, with the pyrite pressed into contact.

A close modern analogy of the wheellock mechanism is the operation of a cigarette lighter, where a toothed steel wheel is spun in contact with a piece of sparking material to ignite the liquid or gaseous fuel.

A wheellock firearm had the advantage that it can be instantly readied and fired even with one hand, in contrast to the then-common matchlock firearms, which must have a burning cord of slow match ready if the gun might be needed and demanded the operator's full attention and two hands to operate. On the other hand, wheellock mechanisms were complex to make, making them relatively costly.

The dog is a spring-loaded arm pivoted on the outside of the lock plate. A sparking material, usually a small piece of iron pyrite, is clamped and held by vice-like jaws at the swinging end of the arm. The dog has two possible positions to which it can be pivoted by hand: a "safe" position, in which the dog is pushed towards the muzzle of the firearm, and an "operating" position, where the dog is pulled towards the operator so that the pyrite in its jaws can engage either the top of the pan cover (see below), or (in the absence of the pan cover) the edge of a steel wheel bearing longitudinal grooves around its circumference. Flint is not suitable as a sparking material in the wheellock because it is too hard and would quickly wear away the wheel grooves.

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Wikipedia