Add the mechanic that pressing alt-fire whilst holding right click (so zoomed in) with either or both Volley Crossbows will either loose a single shot or toggle the firemode of the weapon so that it may launch one bolt with more precision. I understand why you may not want to do that from a balancing perspective, but as the Volley Crossbow for Saltzpyre has less stopping power than his normal crossbow it seems like it would work, we also see that both weapons are capable of single fire, so why not aimed single fire?