I don't know is this is the best subsection i which to post this question. Please indicate me the right place, eventually. And forgive me for not so sublime english, as I'm not a naturally english speaker. Now... I think it's proven that the most effective projectile, in terms of penetration, is a rod. So modern weapons are moving toward Kinetic Energy rounds with a rod penetrator. The penetrator has the problem of tumbling in flight, that is accentuated by rotation, (so all cannons are going toward a smooth bore). The stability issue is resolved by stabilizing fins, as an arrow. Now, if a penetrator was to be fired in vacuum (space), what methods would be used to stabilize it's flight? But most important, would it tumble? And if shot from a railgun, would it tumble?