How to unlock the Swiss K31 in Warzone To unlock the Swiss K31, you’ll need to hit up the Battle Pass for Season 3. You don’t need to pay for it either, just rank it up to rank 31. You can do this on Cold War, Modern Warfare, or Warzone too. Best Swiss K31 loadout in Warzone Now we have the Swiss K31 unlocked, why not give it a shot in-game? This loadout is the best one for aggressive sniping, and you’ll be able to get those one-shot headshots if you’ve got the accuracy to pull it off.