Students today have a reduced appettite for destruction, unlike the Class III potato cannons and funnelators I made in college.
This year I'm doing a ballista (like a crossbow, but the arms are powered by two sets of twisted rope). Don't know how well it will work, as I'm still building it.
My co-workers have an air cannon that can toss a 2-lb fruitcake over a quarter of a mile. You may have seen them on TV.....