Choke works thusly:
Upon bore exit, a shot column will disperse due to aerodynamic effects.
With a cylinder bore (no choke), the drag acts on a wide front of pellets the diameter of the bore. The pictures show radial velocity starting shortly after muzzle exit. The classic 'mushroom'. Dispersion is fairly rapid as the front pellets slow and are pushed to the side by the rear ones.
With a choke, the 'nozzle effect' causes a speed differential, shown as elongation in the pretty pictures. The column is stretched out, and aero forces don't immediately jam pellets to the side as they do with a simple cylinder.
And that's about it.
The WS-1, the Tula, and the Beretta skeet chokes have the interior profile of a converging-diverging nozzle and undoubtedly add an outward radial vector by design.
Inward vector effect is controversial, to say the least.
How did I do, prof?
