User blog comment:BlackTempest/So, energy weapons?/@comment-10390252-20130817201813/@comment-10390252-20130818083732

I think that the spider-droid's guns were probably plasma weapons. Plasma is super-heated and electrically-charged gas so you could do that with the known varieties of Dust.

FWIW - I suspect that there is a 'kinetic' dust that induces motion and possiby a variant of the electric dust that does magnetic effects but we'll have to wait and see. The fact that RWBYWorld physics will be based off of dust means that a lot of the terms its natural philosophers will use might sound closer to alchemy rather than our chemistry and physics.