Unlock Location:
- Progress through the story until reaching Terminus Range Region.
- You will find a Order bunker called Craven's Nook, north of Bones of Sanctuary in the Heart of the Mountain.
- Complete the Bunker and at the end you will find Callous.
Farm Method:
- Defeat Callous inside Craven's Nook Order Bunker.
- After use the Encore Machine nearby to reset the fight.
- Repeatedly defeat Callous until
Atling Gun drops.