Some here seem to prefer ridicule over pertinent information. The dynamics of smoothbore shot is not a new topic. To believe that only modern information or personal experience is valid, proves the height of arrogance. Our ancestors exerted much more diligent study of the topic than is currently being employed... and they were quite educated.
Benjamin Robins wrote the "New Principles of Gunnery" in 1742.
He was a MATHEMATICIAN who revolutionized our understanding of ballistics. His work was based on Newton's principles, pendulum testing, and gunnery fire. His most important contribution was proof that a BALANCED load exceeded all others. He also addressed the FLUID nature of burning gunpowder moving a solid,
and the relationship of the MASS of a load to the bore.
There is much to be learned from old gunning treatises, including the fact that a load longer than the width of the barrel "Flew like a brick," which they knew, because they actually shot bar loads.
The square load is a point of reference, much like the center of a circle or the value of zero. Here is a link for anyone interested in studying testing which infers a principle.
The rest of you can find the same thing by shooting various lengths of cigarette filter with a rubber band. Wonko get someone to help you measure.
http://arc.id.au/RobinsOnBallistics.html 
