Quick question why would you use it
And also can I stick that stuff into a building forgeter missile
Well you could for instance make a gravity-powered gun by having tweezers that squeeze Arcanium extremely hard and can repel something at insane speeds without the amount of matter really that big of a deal (aka bullet-speed RPGs), not to mention you could FUS RO DAH!!!1 in real life. Repulsion bombs that could send people flying. subatomic particles can be forced into tearing through stuff insanely, possibly making new particles in the process, by using the combined electromagnetism and gravity of Arcanium and Gravitanium.
And yes, an Arcanium missile could work well if you can find a way to apply enough pressure to cause a building to not just topple over, but FLY INTO PIECES AND SCATTER EVERYWHERE! If you could muscle up that much Arcanium and pressure.