I remember I tried to make a drone like that and mounted a remote-control tank that shot BB's onto it. (I don't remember how I did it.) I remember I tried to use at an Airsoft match and had it confiscated. To this day, I swear I see a drone in the air almost everytime I drive by that place.
That gave me an idea, I just sewed an IV bag to my drone, and put a needle on one of its rotors like the flamethrower, so I hope it will work because then I can make people pee their pants in an hour with a drone.