Dungeons & Dragons now has a complete gunslinger class, and you can play it now via D&D Beyond. Although DnD has long allowed for the use of firearms, it's never really been designed around them. Guns are a little clunky, especially when you get into the reload mechanic, it's not an avenue that's always worth exploring. Players have long since tried to make their own gunslinger classes, either via creative use of certain fighter subclasses or bringing in homebrew content. But that may change with the release of a new expansion.
The Gunslinger Class: Valda's Spire of Secrets is a new expansion by Mage Hand Press, a third-party producer of DnD content. With six subclasses, nine spells, three feats, and much more, the expansion gives you the full framework you need to develop and play a gun-toting cowboy - no more reverse engineering from the fighter class. It's fully integrated into the D&D Beyond virtual tabletop platform, and you can buy it via the official store.
The gunslinger class, as outlined in the new sourcebook, is as complete as any base DnD class, with tons of options for further customization. There are six subclasses, beginning with the Spellslinger, which...
