Firearms
Automatic Crossbow
What you need: crossbow bolt, clip and automatic crossbow.
Load clip with boltClose clipLoad crossbow with clipCock crossbowShoot target
Wheellock Firearm
What you need: gunpowder horn, lead ball, ramrod, spanner and a wheellock firearm.
Pour horn into firearmLoad firearm with ballPack firearm with ramrodWind firearm with spannerShoot target
Flintlock Firearm
What you need: gunpowder horn, lead ball, ramrod and flintlock firearm.
Pour horn into firearmLoad firearm with ballPack firearm with ramrodCock firearmShoot target
Mechanical Musket
What you need: bullet cartridge and mechanical musket.
Open musketPut bullet in musketClose musketWind musketFire target
Arcane Firearms
What you need: arcane firearm, Arcane Firearms tag, cannot be Berserker Mercenary
use firearm (1-4)fire target
Using Arcane Firearms requires the Arcane Firearms tag, which is automatically provided to Arcanist Mechanists on creation (although there's no way of seeing this since it's invisible in the Tags menu.) You can also purchase it for 1m sovereigns from Lars Gixet in the Tower of Dhond.
To use an arcane firearm, you use it. You can add a number modifier to make the shot stronger. For example, use blunderbuss 4 will make an arcane blunderbuss ready to fire its strongest shot. Stronger settings take more RT to load but the same amount of RT to fire. Simply fire target to fire. It can be aimed at specific body parts, if desired.
Arcane Firearms appear to solely use the Kinesis skill for rolls.
If an arcane firearm breaks, there may be no indication of how it is broken in look (will just show 'it is broken'), inspect, or appraise. NPC repairers will not take it and you will be returned a message saying that your item is not in need of repair. You need to be a mechanist to repair the firearm. Generally, you use a 'hook' tool sold at lockpicking shops. Hold the firearm in one hand and the hook in the other, and repair firearm with hook.