reflection comes back fast

The specialized warhead created a spear-shaped shock wave using the bullet’s air
resistance. Because of that, a lot of the bullet’s speed is taken away by the air resistance.
It was like a bullet flying with an opened parachute behind it.
The shock wave would lag behind the bullet and follow its trajectory. The lag time wasn’t
even one fourth of a second. But in that time, Accelerator had finished healing Last Order,
and at the last moment, he regained his reflection.
In result, the slow-flying bullet cracked open his skull, but he fended off the fatal shock
wave.

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