Brent, as I've tried to explain it's aerodynamic forces that spread a shot cloud.
got that part on my own long ago, no problem.
The speed differential I refer to is pellet to pellet speed difference. All the shot is not accelerated to the same velocity by the choke. The leading pellets are going faster, and retain that differential for a good distance as evidenced by the continuing lengthening of the shot stream as shown in the photos. Even with the increased drag on the leading pellets and the following ones flying in their 'draft' it takes quite a bit of travel for the dispersal to equal what a cylinder choke shot cloud looks like at a shorter range.
This part I sort of disagree with - but only to a point. All fluids in a venturi accelerate the same amount. That said, if you have a string of cars accelerating after a stop light, then the lead cars accelerate first and thus pull away slightly, initially, but the cars further back, like the pellets go through exactly the same process and accelerate in the choke to the same degree.
So, next the front pellets slow down due to wind resistance. I figured that long ago. That however is the same for my two hypothetical barrels in my original scenario. So that doesn't explain choke effects by itself.
Profiles of common skeet chokes are available on the interweb.
All I find are generic, stylized diagrams of chokes nothing like a de Laval nozzle.
