To shoot through those white rhinoceros beetles’ armor, they would have to carry that heavy equipment right up to them. But to remain at a safe distance from those white rhinoceros beetles that had the specs of a tank, they needed to defeat the beetles while staying over 5 kilometers away. They of course could not prepare any means of doing that. And any distance less than 5 kilometers was the same. Whether they were 4 kilometers away or only 1 mm away from the enemy, they would still be shot by those shells the instant they were detected.

Toaru Majutsu no Index New Testament vol.6 ch.6 pt.7