I remember playing with smaller versions of this thing at high school in the early 80's (It was an all boys school. With that much testosterone rail guns and the local all girls high school were appropriate distractions) - Ours would put a 3inch nail through a couple of telephone directories (it was a wooden plank with a load of solenoids on it). We had the same projectile stability issues (cept with us the nail would get stuck in the solenoids). Advantages - potentially rate of fire, but most important (in the case of ours) - no wear on the barrel mechanism - most gun barrels in releasing all that powder and spinning the projectile get really hot and distort, or just simply wear out. Our railgun got warm (when it didn't jam) but suffered no other wear. And yes you could fire anything metal that would fit in the solenoid. Watching the video it would appear that the hypersonic railgun projuces a massive amount of heat to move a large (and unstable) mass - although I wouldnt want to be on the receiving end of the mass I would be interested in see what kind of wear occurs in the barrel. TBF the idea of a much smaller mass ( a needle gun) is a much more sensible idea - however such a weapon (with say fracturing flechettes) would no doubt get banned as an inhumane weapon.