In past versions of Warzone, the Snake Shot ammunition attachment took over the meta for secondary weapons or close-quarters fights. With the Modern Warfare 3 version of Warzone, the shotgun-like ammo has made a return and you may need to try it out.
COD Warzone: How to Use Snake Shot Ammo
To use Snake Shot ammo, you need to equip the Tyr handgun in your secondary slot for a loadout and attach it through the ammunition slot. Unless you find another player’s Tyr, using a custom version of this sidearm is necessary. Nearly every gun in the game has access to ammunition attachments, but only the Tyr and the Basilisk from MW2 can make use of Snake Shot in any capacity. So you may need to get some unlocks out of the way.