I recall reading that gunsmithing was unlikely because they don't want too many guns floating around, which would tend to happen as people craft them to practice.
However, what about bullet-crafting? Maybe alchemy could be expanded to make gunpowder using certain ingredients (charcoal, sulfur, saltpeter). Likewise, smithing could be used to make basic lead bullets, and guilding to give them special propeties (silver bullets?).
Sounds like a lot of work to implement, maybe it's not worth it. It would be fun though.