https://www.gamespot.com/articles/fortnite-drum-gun-added-in-latest-update-patch-not/1100-6460156/

In addition to the arrival of the delayed Playground mode, a new content update (version 4.5) is now available for Fortnite on PS4, Xbox One, PC, Nintendo Switch, and mobile. The update introduces a handful of new weapons to both Save the World and Battle Royale modes, including the recently-teased Drum Gun.

Following the rollout of the 4.5 content update, players can now find and wield the Drum Gun in Battle Royale mode. Epic describes the new gun as a "hybrid weapon that combines the stopping power of a rifle with the suppressive ability and fire rate of an SMG." It comes in Uncommon and Rare varieties, uses Medium Ammo, and can be found in chests, Vending Machines, or as floor loot.