Here's my homebrew write-up for medieval period gunpowder weapons. Feel free to mine for ideas:
Gunpowder Weapons
Simple Melee Weapon
Fire lance, cost: 2 gp, damage: 1d6 fire, weight: 6 lb., properties: Two-handed, smoke cloud, special.
Simple Ranged Weapon
Hand cannon, cost: 25 gp, damage...