History of Deterministic Chaos

Deterministic Chaos is a Void Machine Gun Exotic introduced in Destiny 2: Lightfall.

Overview

Its exotic perk makes the 4th shot weaken enemies and the 16th shot make them Volatile, causing a large explosion. A dedicated mission, What Remains, is set in a stripped-down Garden of Salvation area.

Acquisition

1. Finish the Destiny 2: Lightfall campaign, then speak to Nimbus on Neomuna to start the quest Unfinished Business (after paying respects to Rohan in the Hall of Heroes).
2. Per TheGamer, the quest has you collect Cipher Qubits from Vex on Neomuna, trigger a Vex pylon at Maya's Retreat, clear the Thrilladome Lost Sector in Liming Harbor, defeat Cabal in Ahimsa Park, and then complete the What Remains mission, where you work through Vex wheels, laser cannons and Taken Blights to claim the weapon.
3. Return to Nimbus to finish.

Once owned, it can be picked up again from the Exotic Archive at the Monument to Lost Lights (not verified in this pass).

Catalyst

The catalyst gives Fourth Time's the Charm, returning two rounds to the magazine on rapid precision hits. Sources disagree on how it drops (Exotic Orders or ritual activity rewards vs. a quest); verify in game.