Here are a couple of charts that make the size thing clearer:
Another factor is the number of pellets(rounds) in each shot shell.
Then there is pattern dispersion at
x feet out from the muzzle.
Othe factors for consideration involve energy transfer (determined by velocity and pellet(round) weight(mass), shot pattern at anticipated distance and target cover (clothing, walls, windows, car-door, etc).
Even a .410 loaded with the appropriate shell is a devastating tool.
Good info. And I agree with your comment:
"Even a .410 loaded with the appropriate shell is a devastating tool."
My first gun as a single-shotter .410.
But there is a school of thought that a 12 gauge with 00 buck or slugs is the sine qua non of home defense. But based on many factors, I think No. 4 buck is a better load, and that for home defense 20 gauge is better than 12. Lastly, I "love" that bullpup configuration for home defense. Much more maneuverable in the "tight confines" of a home situation.