The principle behind the antihail cannon is to prevent the damage cost by hailstones by eviting their formation and growth by melting all together. Thanks to shockwaves which emanate from the hail guns, the supercooling water situated on the external layer of hailstone is transformed from liquid state to solid state. Therefore the hail nuclei are not able to melt anymore and remain at a small size which thus prevent them from inflicting damage when they hit the ground.
On the early 1900s, hail cannon shockwaves were generated by gun powder, which was both dangerous and take a long time to reload. At those days, a much greater number of cannons needed to be deployed in order to adversely impact the formation of hailstones.
Today, hail cannons generate their hail disruptive shockwaves through the use of acetylene or butane gas which allows for the emission of a more powerful shochwaves and a greater rate of frequency which greatly improve their efficiency in the prevention of hailstone formation and growth.