Warmatrix

Arquebusier, from manual by Jacob de Gheyn

The matchlock was a major improvement to hand-held firearms like arquebuses and muskets. It was invented in the early 15th century CE and became widespread around 1450 CE.
In a matchlock mechanism, gunpowder was held in a 'flash pan' a.k.a. 'serpentine lock' and ignited by a slow burning match. This allowed the gunner to hold the gun with two hands, greatly improving his aim over older handgonnes. Despite its advantages, matchlock guns did not replace handgonnes right away; the two co-existed into the 16th century CE.
Around 1470 CE, gunpowder quality was also improved, when gunners switched from 'serpentine' a.k.a. 'mealed' powder to crumbled and corned powder. This deteriorated slower, was less vulnerable to moisture, ignited quicker and more evenly, and packed 2 - 3 times more power.
The combination of matchlock and crumbled gunpowder gave rise to a new kind of gun: the arquebus, also called harquebus, hackbutt or hook gun, because it had a hook-like butt. The butt and the name had been developed earlier, though became more important with increased firepower. So much, that the name handgonne started to disappear and was replaced by arquebus. Its barrel was about 1 meter long and the gun weighted some 5 kilograms. It took between ½ and 2 minutes to reload and could penetrate heavy armor at close range.
Around 1510 CE a larger and heavier type of arquebus appeared, the caliver. This type had more firepower and accuracy, effective to about 100 meters. It co-existed with the older, lighter arquebus.
By the 1540's CE the gun was further lengthened. This became the musket, about 1.5 meters long and 10 kilograms in weight. It required a fork that was planted into the ground, on which the end of the barrel could rest. It had more firepower and was effective up to 200 meters, but was slower to reload, 2 - 3 minutes on average. The musket could penetrate heavy armor even at medium range. However it was a heavy load to carry.
Because there were no strict standards, arquebuses, calivers and muskets were often confused with each other. This was aggravated by further developments. In the 17th and 18th centuries CE, the musket gradually became lighter, though not much shorter, until it replaced the arquebus as the main portable gun.
Matchlock guns like arquebuses, muskets, musketoons and blunderbusses existed side by side with older missile weapons. In the second half of the 16th century CE the matchlock was superseded by more advanced firing mechanisms like the wheellock. However it remained popular up to about 1700 CE, because it was cheap, simple and widely available. Only the invention of the flintlock rendered it completely obsolete.