electromagnetic gatling gun is a really dumb idea in reality without an extremely powerful power source.
a gatling gun only rotates because it needs to eject catridges (which it does in the manga but shouldnt irl) because they would auto fire the moment you push the entire bullet in the barrel if the power is held on. An EM gun does not need to cycle its barrels.. Also, an EM gun typically requires a capacitor to super charge between shots limiting its rate of fire, and if the power source was powerful enough that this isn't needed, you need some serious metal to withstand the temperature generating from using the gun.