teh Saiga has the potential, but hasn't been released yet, as far as i know.
Remington also makes a "home defense" version of the 870 20ga that features a +2 magazine tube extension, for a total of 7 rounds, IIRC.
Anywho.... he was running a course with a shotgun a little later in the show
and the gun he was using had the magazine tube extending well beyond the muzzle.