I'm curious as well. My first guess was that the explosions are coming from the projectile punching through those walls they put up, or the speed of a projecti

I'm curious as well. My first guess was that the explosions are coming from the projectile punching through those walls they put up, or the speed of a projectile superheating the air through which it's travelling to the point of igniting the air around it. The latter guess seems way off base, but I'd love to learn exactly why!