Skull-40 Attachment Guide
The Skull-40 attachment in Call of Duty: Modern Warfare 2 and Warzone 2 is Weapons Platform Specific. In other words, this rear grip is exclusive to a particular family of weapons.
How to Get the Skull-40
To unlock the Skull-40 attachment in Call of Duty: Warzone 2.0, you need to upgrade the FJX Imperium to Level 22.