There is no dearth of special weapons that you will find in Fortnite, and the Ex-Caliber Rifle is one of them. As a part of the 14 Days of Summer event, you need to find and use an Ex-Caliber Rifle to deal direct damage to an enemy.
This challenge can effectively be broken down into two parts, one where you look for the weapon, and the other where you use it to deal damage to an enemy. The former isn't exactly tricky, but it's the latter where things get difficult.
Where to Find an Ex-Caliber Rifle in Fortnite
Since it's a weapon that's associated with a challenge, it's rather easy to find the Ex-Caliber Rifle in Fortnite. To pick one up, all you need to do is loot the regular chests that you find while exploring the different POIs on the map. This weapon comes in different rarities, and the higher rarities are harder to come by.

So, to have the best chance at finding this weapon, head to a POI with the highest chest spawn rate. Additionally, you can also loot it from enemies you've killed, but for that they need to have one on them.
How does the Weapon Work
Whenever you shoot the Ex-Caliber rifle, it fires a huge sword that causes an AoE explosion where it lands, dealing splash damage to anyone caught in the radius. However, if you hit someone with it, and the sword lands on the enemy, then they'll take regular penetration damage, and the explosive damage.
It's a high damage weapon, which lets it make up for whatever it loses out in its rate of fire. To make the most of this weapon, pair it with a shotgun or a fast-firing SMG, which also happen to be the best weapons to use in the Blitz Royale mode.
How to Land a Direct Hit With the Ex-Caliber Rifle in Fortnite
Since it's a slow firing weapon and fires a big projectile, you can complete this mission in two specific ways. Either you go really close to an enemy and shoot them with it, or you take a vantage point and unload on whoever you see in the horizon. It doesn't have great range though, so don't try landing a direct hit on an enemy from too far.
It's absolutely disastrous to try and shoot someone up close and personal because chances are you might take a shotgun to the face. So, its best if you stay at a distance. You'll know you've landed a direct hit if you see two damage numbers. The second one arrives after a brief delay though. There's set damage requirement to complete this Fortnite 14 Days of Summer challenge with the Ex-Caliber rifle, just landing a hit does it. And if you're successful, you get 5k XP as a reward!
If you're ready for 14 Days of Summer, make sure to also check out the Fortnite x Squid Game Crossover on Pro Game Guides.