[Wonder Warthog]

That must be the guy, and I must have mis-remembered the specific size of buckshot. Heck, I read the story in an “outdoorsy” magazine in a barber shop going on forty years ago.

[Tainan]

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.