Visualize a cone shape, an elongated triangle in two dimensions, with the wider base farthest away from the muzzle. This is the traditional pattern for the dispersion of case shot bullets.
Now, chop off the two angles of the wide base of the cone/triangle to about mid point on its sides and what you will have is a four-sided diamond-shaped pattern of dispersion although the angles/sides of this diamond are not equal.
Of course, this pattern is not as regular, as the dispersion from every round will vary but I think the point was that those bullets that travel along the axis of the bore will go farther than those that do not.
The result is that, GENERALLY, the shape of dispersion of case shot bullets is not a cone, as commonly assumed, but an elongated diamond.