"I don’t think we can," Harry said softly; Draco’s expression pinched further, "I became the master of the wand because I disarmed you. And you became the master of the wand because you... you disarmed Dumbledore," he slowed as a thought occurred to him, "But none of this matters, because he doesn’t even have the elder wand yet. He’s still using his own wand," a spark of realisation, "And I’ve already disarmed him at the Graveyard!"