The drag vector on the individual pellets.
Once the drag force on the shot mass leading edge slows the leading pellets the trailing pellets push them out of the way to all sides and this starts the dispersion.
Once it starts, it's accelerated by the drag vector on each pellet.
The more out of plane it gets, the more side force.
The universe is not expanding. Redshift is not entirely recessional velocity. There is no 'dark' matter. L-CDM cosmology has been refuted over and over. 'Big Bang' is indistinguishable from creationism, and in fact was first postulated by a theologian. L-CDM cosmology depends entirely on the 'given' that the universe is both homogenous and isotropic. Observations show that it is neither, on any scale. The universe is alive. Galaxies have a life cycle just like animals do, and the material is recycled over and over. An active Seyfert galaxy almost certainly creates matter, so entropy need not cause an eventual end to the universe. This a stranger place than we can know at present, and the whole picture may be beyond human understanding. I'm certain there are aspects to reality that we cannot perceive. Enough?
