First, a little historical background from the wiki
The first representative of explosives was black powder - a mechanical mixture of saltpeter, coal and sulfur, usually in a ratio of 5: 3: 2. There is a strong opinion that such compounds appeared in ancient times and were used mainly as incendiary and destructive agents.
Since ancient times, saltpeter for the manufacture of gunpowder has also been obtained artificially - by handicraft in the so-called saltpeter pots. These were heaps made up of plant and animal waste mixed with construction waste, limestone, and marl. The ammonia formed during decay underwent nitrification and was converted first into nitrous and then into nitric acid. The latter, interacting with limestone, gave Ca(NO3)2, which was leached with water. The addition of wood ash (consisting mainly of potash) led to the precipitation of CaCO3 and the production of a solution of potassium nitrate.
To create guns and pistols, I suggest adding a new skill: gunsmithing

Crafting recipes that I offer
Mulch + limestone = saltpeter
Saltpeter + brimstone + coal = gunpowder
Gunpowder is a basic item that unlocks other gunpowder technologies if you have the necessary skills.

wood+hard metal = arquebus
The arquebus fires similarly to a bow, but takes time to fire (while the fuse is burning). Must be loaded and ignited before firing.

wood + wrought iron + flint = Flintlock gun
The flintlock gun fires almost instantly, but requires additional skill
gunsmithing.

wrought iron + flint = pistol
Works similarly to the Flintlock Gun, but takes up one hand and does less damage. Also requires gunsmithing.

hard metal + steel = cannon
Building. Works similar to a catapult, but does more damage. Also requires gunsmithing.

nugglet of lead = bullet
Necessary for shooting guns, arquebuses and pistoles.
cast iron = cannonball
Required to fire a cannon
cast iron + gunpowder = bomb
You can shoot them from a cannon. In this case, damage is dealt in a radius from the point of impact. Can be placed in a cave: clears space in a radius and causes collapse.
clay+gunpowder+tar = Grenade
Throws similarly to snowballs. Deals damage within the radius of the hit.

The point of gunpowder technologies is that they are more expensive, require a rare resource (sulfur) and a lot of metal. At the same time, they allow those who were able to master them to achieve greater destructive power. They can also make useless lead more useful.