How advanced could someone make a firearm with Medieval Technology

Assume I have someone who doesn't age, and has a lot of time to learn any skill or experiment with things, but who was born and raised (prior to becoming ageless) in a medieval farming village. He is of above average intelligence, and, because of his ageless nature, money is hardly an issue (he has mastered enough skills to be able to sell high quality work in a number of fields for significant prices).

How would he go about developing firearms from medieval technology (say around 1000-1200 CE)? How advanced could he get with them without basically starting the Industrial Revolution (basically what could he do on his own)?

I am particularly inspired by the 1632 series and the French creating rifles using a different chemical compound for percussion caps, but I don't understand most of the chemistry involved.

EDIT: In response to comments, let's assume we are looking at a timeframe of between 400-600 years of him being around. What could be accomplish in that time, starting from the tech level of 1000 CE.

As for what I mean by advanced, how effective of a weapon could he make? Would he be able to create something like a Sharps rifle? A Springfield? A Gatling Gun? A Repeating Rifle?

posted about 6 years ago

Marshall Tigerus‭

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