The Forgotten Realms and the Sword Coast have never had a gunslinger class, or any such variant. While there ARE areas of Faerun that allowed for black powder (the Eastern/Asian realms for example, or Gondian Inventions)) even they were generally restricted to cannon or siege type weapons - black powder tended to be more of a defensive "trap" type or offense siege type usage.
While appropriate for some steampunk or pirate type RPG's - Arcanum and PoE come to mind, it's not lore/realm appropriate here.
