Replace all the files in patchday3ng folder to 
mods/update/x64/dlcpacks/patchday3ng/dlc/x64/models/cdimages/weapons 


Replace all the files in patchday4ng folder to 
mods/update/x64/dlcpacks/patchday4ng/dlc/x64/models/cdimages/weapons 


If u wish to have empty grip 3d model u can replace the files EMPTY GRIP
( Invisible ) to mods/update/x64/dlcpacks/patchday4ng/dlc/x64/models/cdimages/weapons 