pebble railgun

Accelerator ignored him and purposely crashed down onto the asphalt below. The
impact caused pebbles to pop into the air; he flung out a hard, two-stage kick at them.
A tremendous roaring noise split the air.
The pebbles, their vectors altered, flew out faster than a Railgun shot, but disintegrated
just four or five centimeters later. But the shock wave remained; the speed had already
broken the sound barrier. However, Kakine, putting all his strength into his white wings,
used them to disperse it. Their respective waves clashed between them, and the
resulting surge of air ripped signboards and traffic lights from their fixtures.

- Toaru Majutsu no Index Volume 15, Chapter 5 Part 3