cpa we are interested in the deformation of shot because it is accepted that deformed shot affects patterns and causes shot stringing.
In your example of a barrel with a bore diameter equal to diameter of a single pellet, say #8 and one ounce, the bottom pellet of that shot charge would be under much higher stress than a shot on the bottom of a shot column of 1 ounce of #8s in a 12 gauge. Just like the feet of the bottom acrobat in Case 2.
Isaac Newtons laws of physics, at the velocities we are talking about, are the theory, and much of the modern technology has developed using them. People like Bob Brister and John Olin and Tom Armbrust have done the empirical experiments that validate shot stringing and shot deformation. They proved that harder lead shot (with antimony) strung less that softer shot. The theory being that it deformed less and so had a lower coefficient of drag than shot that was more deformed. The painted shot test proved that the bottom third of a shot column deformed more than the top layer. So the experimental confirms what the laws of physics predict.
If you build a shotgun where one ounce of #8s will cover the bottom of the wad in one layer you will have much less stress on that single layer shot compared to your shotgun with a diameter of one #8 pellet shooting one ounce of #8 shot. I suppose the shot column in the cartridge could be 6" long!
In your theoretical shotgun with a bore diameter equal to a #8 pellet the pellet at 1/2 the length of the total shot column length will see the 1/2 of the stress of the pellet at the bottom of that shot column.
