Remote control drones are easy enough, but a proper drone that auto fires? Not easy.
Most I've seen, like the paintball one, work on a fairly simple webcam based motion tracking system. Some will even be 'advanced' enough to fire only at human like shapes. I have yet to see something produced in the private sector that will stop itself after shooting its target, let alone one that will be able to hold fire on an unsafe target or an already dead target.