Do the GRA Mods only work on GRA weapons? Because I got a few mods for my Plasma Pistol from the vanilla FNV and they couldn't be added. So I'm thinking, can the mods only be added to GRA weapons - as in I have to get a GRA Plasma Pistol to add the mods? Or is this a glitch?

Yes.



Nope, it's how it was intended. Well, actually it's how the game engine forced Obs to work around it, but the result is the same.