Book 2, page 21, "This Skill allows a character to restore Durability to firearms given time, equipment, and parts. It also allows a character to lay down specifications for parts of firearms to be produced using other Skills such as Machining. Each point of Durability requiresa unit of parts, a Tool Kit2 and the accomplishment of 10 Task Points."
If Firearm Repair crafting materials are not available they can be made by a machinist. Machining is not required to fix firearms, but it is required to make the parts.
No character has Firearms Repair, Modern, or Firearms Repair, Primative, or Machining.
Note to Players: Information here is considered metagaming. Your character should not reference or use these numbers in game to determine who should roll for specific skills.