I was thinking of using the FLAK 88 for the armed drones higher up since the city declined my permit for a missile battery. If fact, they even have an ordinance banning the discharge of BB/pellet guns.....
My Army unit had one of their 3inch anti-tank tubes (firing 75mm blanks) that every so often would emit a perfect smoke ring. At about 100ft out of the barrel it would be about 30ft in diameter. Never had a camera ready when it would do that, darn.