I definately don't think I would go any bigger. I think what your are using right now would work more than fine and if you are accustmed to using the 180's stick with it. It really doesn't take a whole lot to take down a calf moose. I have taken 3 calves in my days and have never seen one go more than 20 yards after cracked with a .308 using 165gr i think it was.