Do you mean outgoing or incoming? Considering that it's upgraded from return fire, I guess it's incoming damage. So, that makes this item a bit too specific. Is the idea to buy this item and go full spirit resists without bullet resists?
Anyway, I think since this item could have negative impact if not used properly, that's not a very good idea. However, if you want to dodge bullet damage, it could be a straightforward upgrade from return fire. Return fire gives 50% bullet damage and 25% spirit damage reflected. So, this item probably may have 80% bullet damage reflected and 40% spirit.
But now when I think of it, Colossus will become not viable choice over this item.
