You might need some form of archive invalidation to make them appear I recommend launching your game with Fallout Mod Manager (which you should be using anyways!) To install, just unpack the 'textures' and 'meshes' folders in your New Vegas/Data folder.

The project replaces the textures on almost all the weapons, making each one look a lot nicer and more detailed. Weapon Retexture Project is a mod for Fallout: New Vegas created by Millenia.