Submission + - The vortex gun - coming soon to a protest near you? (dvice.com)
A vortex gun uses a pressure wave and a carefully designed barrel to fire donut-shaped rings of air that can hold themselves together over long distances. The military (starting with the German military during World War II) has been running experiments with using vortex canons to knock things over, but it's not a particularly efficient or effective way to go. What the gas rings can be used for is transporting other gasses (like pepper spray or tear gas or pesticide) long distances with a decent amount of accuracy, holding their cargo inside the calm center spinning vortex