Or a .243...
.243 would indeed do some damage, but the .30-06 would do a bit more at longer ranges. A .300 Win Mag or .50 Cal (BMG) would be all the better.
Barring an ongoing conflict or security concern, each and every citizen should feel obligated to bring these things down if they are just flying them up there watching us for no reason at all.
Perhaps we should make ‘drones’ of our own......