Radio Psychedelica

It should be possible to fire a potato cannon from a potato cannon, giving a two stage effect.
Slipping 1" ABS pipe inside 2" ABS would work, although I'd have to glue on a rubber strip as wadding.
Or go to a larger (4", perhaps) outer barrel, and a sabot style round?
Firing the second stage would be difficult, as a few fractions of a second delay would be needed. Perhaps a capacitor delay circuit, firing a ignition spark would work, and certainly would be light and simple.
It certainly would be dramatic, with a midtrajectory muzzleflash.

Perhaps I need a firing range.
(RenegadeMime suggests a leash.)