Fire Bomb is an alternate Pack-a-Punch ammo-type found in Call of Duty: Black Ops 4, and it has a chance to be applied to an upgraded weapon when placed in the Pack-A-Punch Machine again. It costs 2500 points initially, but lowers to 1500 after upgrading your weapon 4 times.
Fire Bomb ammo has a chance to ignite many zombies at once. It causes the zombies' eyes and mouths to light up in a lava effect a few seconds before dying. Fire Bomb ammo is super effective against Lightning Catalyst zombies, causing them to explode in a high-velocity blast. It is also a necessity in order to complete certain Easter Eggs.