Thank you Oskan one! *Cheers the man on!*. Repelling force, in magnitisim's case, would mean somehow applying a uniform charge to the iron so that it was all charged the same, negative or positive. Otherwise, the iron just realigns and keeps on coming, likely faster. And not all metals are magnetic. I COULD just shoot you with copper, silver, or gold. Or lead. or Titanium. Or many others. Also, Electric repelling/attraction would work much better, either way. First you ionize your target, then you ionize the weapon in the opposite direction. Problem with it is it would be blocked, easily, by atmosphere.
Also: There are no moni-pole magnets.