In Fortnite Chapter 3 Season 1, Lt. John Llama will sell you the Boom Sniper Rifle for 600 Gold Bars. Currently, it doesn’t spawn anywhere else, so you won’t find it lying around or hidden in any chests. The only other way you might get a Boom Sniper Rifle is if you eliminate a player who has one.
Lt. John Llama can be found at the Llama Homestead, a cabin at the southwest of the Logjam Lumberyard and west of Crackshot’s Cabin (otherwise known as the Nutcracker House or Christmas House). This is also the location where you’re guaranteed to find a Supply Llama in every match unless another player gets there first.
The Boom Sniper Rifle is an Exotic version of the Heavy Sniper Rifle, which fires explosive clinger rounds. It also has a higher magazine capacity than the Heavy Sniper Rifle, so you can fire five shots before reloading instead of just one. The initial impact of a Boom Sniper round is only 10 damage (25 for a headshot), but the explosion that follows a second or two later does 60 damage, bringing the total damage per shot to 70 for a body shot and 85 for a headshot.