Gregory's ServerHeavy shotguns are a countermeasure against enemy killer drones/bombs, not looker drones.
If you want to take out lookers, anti-drone drones seem to be the most promising approach for now. A 30mm smart round could easily be more expensive than the target, and also more expensive than an anti-drone drone.
@isaackuo @graydon @cstross
Those quadcopters make quite a bit of noise. I can imagine cheap mini missiles might be able to target them by their sound.