1- Run OpenIV and toggle Edit Mode
2- Go to: update > x64 > dlcpacks > patchday3ng > dlc > x64 > models > cdimages > weapons.rpf.
3- Drag your files to here
4- Click: file > Rebuild and Rebuild again.
Credit to Jotape17 for converting the model to GTA V
Credit for me for modeling and texturing