What kind of weapons are intendend for this target? I assume that are rifles, due to the distances used. All rifles have enough power to throw a projectile at supersonic speeds? Or only the more powerfull ones? That can make difference when building the sensors.
Anyway, the person that presented the target said it was "old technology" and I remember that when I searched about electronic targets most (or all...) the vendors used optical sensors. The problem was identifying when one shooter hit his neighbor's target, shrapnels, things like that.