Shotgun pistol (Evanix Rex?)

At. 45 caliber, turning the Rex pistol into a shotgun would make for an interesting little snake gun while hunting. Give it a smooth bore and it would be close to a .410. While many snakeguns are single shot, I would like a followup shot though. Maybe a double barrel derringer version, but that would make it even bigger. So maybe something purpose made. 

What do you think, could an airgun snake gun be made that is effective, yet small enough to be practical, perhaps even as a side arm to be worn while hunting or fishing?