Good question! I was thinking of the three guns as a set of assets that would be used together in the game and one large texture is much more efficient for performance than several smaller textures. If they were to be used separately or if one would show up without the others though, separate textures would work great.
I used the UV Packmaster addon and it saved my bacon. I had started out doing it manually and it was a nightmare 😄 I literally spent a whole day or two just unwrapping and packing before discovering the addon.
