Well, I'm not sure how to particularly explain Volume. It's something you try your best to define. Like how can I make the shades pop the object out rather than the outline. The 2nd sword is what I interpret the volume of the object to be based on your initial sword.
The good thing about your first sword was that it DID define some kind of volume. The initial issue I had with it was that it didn't follow the "squarish feel to it" Yours felt as if the middle meaty part of the blade kinda pointed out towards. Anyway, the only issue with the volume of your first sword was the top and the bottom part of the metal. Am I making things any clearer?