NOTE: You need to equip the augments “Starlight” and “Starburst” onto your Fire Works ammo mod for this to work
Step 1 – Train a horde of zombies until they stop spawning
Step 2 – Attack the zombie that’s in front of the horde until your fire works ammo mod procs
Step 3 – Right when you see the fire works spawn into the horde, use your field upgrade and the fire works will begin exploding right after you used your field upgrade