Darryl:
That's an interesting 'twist' on an old concept, discovering a modern use for a vintage feature. Of course there were no plastic wads or shotcups in existence during the heyday of straight-rifled bore-guns.

I'd be interested to hear more about plastic shot-cups taking on a spin when fired down a smooth bore. How much spin? If this could be harnessed or controlled, it might be a way to open patterns deliberately. Of course, we should always be mindful of the 'urban myth' of spin-stabilisation in 'rifled' shotgun slugs!