In the first Mistborn novel, it's explained that one key rule of Allomancy is that it can't affect metal in or attached to other people's bodies.
However, in The Hero of Ages, Vin seems to be able to do this:
"She Pushed outward with a sudden wave of power; Inquisitors were thrown back by their spikes." (pg. 650 in the paperback box set edition)
Does duralumin let Allomancers break this rule? If so, did I miss an explanation about this earlier on?