In order to receive a bonus from your Event Weapons during an event, you must match the Event Weapon to the type of Event that is ongoing.

ie: During a Blight event, only Blight Event Weapons will provide bonuses. If you are using a Deadhaze Event Weapon, you will not receive a bonus for that event mission.

Event Weapons contain the name of the type of Event that it matches to, which allows you to quickly and easily see which Weapons to equip during a particular Event.