From Slate.com:

While the technological ingenuity and legal maneuvering of makers such as Wilson and Imura may strike us as quintessentially modern, in fact the work of these garage gunsmiths hearkens back to the first experiments with gun-making in the late Middle Ages, an era before firearms became the province of corporations—and centuries before their subjection to any kind of government regulation or oversight.

The story begins with that most dastardly of medieval inventions, gunpowder, first developed in China probably during the Tang Dynasty before gradually making its way to Western Europe by the middle of the 13^th century. Initially the use of gunpowder weapons on the medieval battlefield was limited to larger artillery pieces such as the pot-de-fer and theribauldequin. Soon, though, gunsmiths began experimenting with smaller, increasingly portable weapons that could be carried more easily across a battlefield.