You need OpenIV to import the Weapon
1. Make sure that you are in the edit mode
2. Navigate to mods\update\x64\dlcpacks\patchday8ng\dlc.rpf\x64\models\cdimages\weapons.rpf\
3. Move the modded files in there
4. start the game and enjoy!
Added a Magazine
Fixed a bug where the mag release moves while reloading in first person.
Vinx: Converting the Weapon to GTAV
Papyrusan: Modeling and textureing the Weapon.