When two magnets with concordant poles are approached, to the release of one, the other is launched at a discreet distance and accurately toward a metal target. It works like this:
A gun that launches magnetic darts or neodymium magnets that you can view at the left of the photo "Chain of darts". There's a trigger and the barrel on the right from where escape the darts.
They fit darts left inside the red cylinder you see and automatically are drawn into the firing barrel. By pressing the trigger, the first of the series is moved away from the previous and pushed into the barrel from which it is ejected and released about 6 meters away. Releasing the trigger, this returns to its starting position, while the darts train advances taking in the vicinity of the barrel, and then the cycle continues. All without the use of springs or compressed air, but only with the magnets. The transparent structure has been realized in 3D printing as well as the inside mechanism.
Currently I use it as a shooting mark on a "Target Shooting" metal, having regard to its accuracy. The magnetic darts thrown at the shooting range, are being held back by this metal.