Railgun fires metal objects at incredible speeds using electricity. The size of the object limits the Railgun's effectiveness as smaller objects melt from friction with the atmosphere at a certain distance. While larger projectile and yields more power and can travel further they do so at a much lower speed. Either way the destructive capability of this technique is described as building buster, it also superheats and ignites the air (depending on the speed which are said to reach mach levels).
The name somewhat contradicts the details of how an actual railgun functions, though, as it doesn't use "conducting rails". Although a rail gun is really just two rods using the right hand rule and conducting electricity to propel a projectile. This however still contradicts as it doesn’t require both arms to use.