The Weapon Customize Extension by futoshisan that was removed some time ago from the nexus, I mean no offence to the author re-uploading they're work, and if asked to do so I will take it down immedietly, this was a mod which I had a ton of fun with when I first got Metal Gear TPP.

It is incomplete in that not all attachments are included, some are even removed, this includes some of the underbarrel grenade launchers, underbarrel shotguns and pistol muzzle accessories, hence why I put it in modders resource.

It's in a snakebite file and it's perfectly safe to use (bar the missing attachments), but if you want to edit it or improve it in any way then you can just as easily open up and edit the MGSV file