Drop the "Nepgearsy Hydra Weapon Case" in your mod_overrides folder located here:

C:\Program Files (x86)\Steam\steamapps\common\PAYDAY 2\assets\mod_overrides
or
C:\Program Files\Steam\steamapps\common\PAYDAY 2\assets\mod_overrides

If you don't have one then create one in the "assets" folder.

Credits: Nepgearsy for the weapon look, Matthelzor for making the retexture and some additional stuff to it.

Changelog 1.2 - Added support for mipmaps (mostly made for low-end pc users.)

Changelog 1.3 - Added mysterious envelope, also added default CAR-4 as optional choice.

Changelog 1.4 - Removed TPS textures, decreased size by a little. Thanks to Oku for pointing this out!