Well, it would obviously be balanced just the same as before, but it would add a pretty badass psychological effect to see two muzzle flashes, two empty hulls ejected, and two shells loaded each time you cycle the action.
I.E. The gun would still deal the same damage, except it would consume two rounds each time it is fired, and will hold twice as many total cartridges. This *is* taking place in the future, after all.
