If the weapons are truly smart, who has any use for an omni-directional blast like a grenade? Keeping with the ball form, it is more likely it would hop and shoot tiny bullets into the forehead of everyone in the room; it could use the same exact tech that cameras now use to auto-focus on faces (until everyone started wearing decoy faces, ala numerous examples in the animal kingdom).

One "Little Boy"'s tonnage worth of gun-toting quadricopters dropped on a busy city would probably result in more deaths than Little Boy itself did.

(the world is pushing heavily in these directions; scary stuff)