Storytelling and Lore aside -- early firearms are kind of a bad idea in my opinion. If you are playing a game in a very "medieval" setting, guns would be so bad to the point where their disadvantages would COMPLETELY outstrip any in-game reason to use them.

If you make them too powerful, well, a majority of rich and or powerful people will hunt your gun DOWN to discover it's properties. Now you suddenly have a game where a technological revolution just came out of nowhere and suddenly ogres are using Mosin Nagants.

These two things aside, my biggest point is how matchlocks/flintlocks were used in real life. They were used for the economics and practicality of things. Flintlocks were the norm/successful because fighting was done in large scale regiments, where individual reloading time/marksmanship is less relevant. Not only that, but the men in these regiments could be drafted from the most lowly of places, yet they could still contribute to the fight even if they were nearsighted and horrible at using a bayonet. They put lead down range. So why would a "hero" use this type of weapon? They wouldn't -- because characters in DnD aren't common soldiers, even at level 1, they are a elite fighters at the very least.

What I am getting at is that if you aren't a common soldier the simplicity of a flintlock musket outstrips itself and many different weapons would be more useful. This includes medieval bow technology, and more importantly if guns DID exist you would have an artisan gun, at least a highly accurate rifled musket, with a good action. Or of course something really good at the time, like a matchlock 5 shot rifled musket.

So just go with bows and pistol crossbows. If you REALLY want firearms in there, you need (from a lore stand point) to be that firearms to at least some small extent are known in this world, and your firearm player character even at level one has an elite rifled musket or highly prized pistol etc.

Sorry for word wall.