No one can tell if going to a 165 will make your gun more or less accurate.Each gun has it's own preference that can only be discovered by trial and error.Go with whatever load shoots best in your gun but the 150 will kill deer just as well as any 165gr will.It is normal for group sizes to be twice as big at 400 yards as at 200 yards so your kill percentage on woodchucks will drop off at longer distances.If you have an accurate load already there is no real reason to change.