A player wanted to use the firearm to kill enemies, I allowed. He used wit to roll. But, I couldn't find anything in the PDF about using the firearms to kill enemies. How do you see this?
Firearms, like any other item, can affect the fictional position. So, they can be used to kill enemies if that makes sense. Maybe some enemies are too fast to be hit by a bullet, and the GM will say it's a "risky/limited" position and the players need to use extra resources to have a major impact in the scene. But, yeah, firearms can definitely be used to hit enemies.