The firearm rules are available in the free version of LOTFP on Drivethrurpg. They are OGL so I will probably include them in Guns of War as well.
As a very quick summary:
- All gunpowder weapons deal 1d8 damage
- Pistol range: 25’ / 50’ / 100’
- Arquebus and Musket range: 50’ / 100’ / 200’
- Double range and penalties and no DEX bonus at Medium and Long range, unless Rifled
- Matchlock/wheellock reload requires (10 rounds + ENC - DEX mod)
- Flintlock reload requires (5 rounds + ENC - DEX mod)
- Pistols and Arquebus ignore 5 points of armor at close range
- Musket ignores 5 points of armor at all ranges
- Musket has -2 to hit unless used with resting-fork
It makes me want to play an Age of Pirates game, personally.