I still think a pump shotgun is a far superior close in weapon, especially in terms of how much damage it does. Put a 3″ magnum buck load into one of their grapes and its Jackson Pollock time.
How about an ‘semi-automatic’ shotgun (no pumping needed between shots). Some of the ones made are ‘inertial’ based. This means that they use the ‘kickback’ of the shell to load the next round as opposed to using gas bled from around the discharging round.