Thank you for the kind words. Glad to share any info in my posession.
While I agree with Roster that your model would be difficult, let me add a bit of fuel to the fire. IMO, shot acts as a fluid in the choke constriction. That is, it is experiencing internal pressure due to the powder gas pressure behind it and the pressure of the air being forced out of the barrel. The shot can't support shear forces, but is confined by the barrel. As it exits the muzzle, the shot pieces "push off" of each other as the relieve the pressure they are under. Some of the "push-off" is in a sideways direction and causes pellets to depart with a small sideways velocity, along with their axiel velocity. This sideways velocity is what we see as dispersion. Further, the air trapped within the shot column is pressurized and expands as soon as the shot clear the barrel. Some of the expansion creates a "sideways" wind that also imparts some sideways velocity to the shot pieces.
Now, the good part. When a fluid flows through a constriction, such as a choke cone, the velocity must increase to maintain mass flow rate. The increase in velocity comes at the expense of pressure; the pressure drops. The drop in pressure reduces the pellet to pellet push-off and the "sideways" wind. Therefore, dispersion is reduced. We know that the velocity of the shot charge is incresed by about 1 fps per 0.001 of constriction. So, the increase in velocity is confirmed.
That could be helpful in your model.
