WOW, I discovered this magnetic effect almost by chance by testing for another experiment. it is amazing how fast the arrow is shot from the magnets with hole. To obtain the weapon effect, the arrow and the launcher must have the same polarity. If the polarities are opposite you still get a nice effect like a tractor beam.
The magnetic fields of the dart and of the launcher interact with each other. When the dart is located exactly in the center of the launcher the attractive and repulsive forces are in balance and contains a high potential energy (the same amount of energy that I used to let the dart into the launcher). when I push the dart the system exits from equilibrium and the repulsive force prevails over the attraction, and the dart is fired.