I would define self defense as inside your house and at close range under a life threatening situation.
Cool, calm and collected? Probably not.
Give me a 12 gauge with an improved cylinder barrel loaded with number 4 or BB birdshot. This will not penetrate like buckshot or slugs (these require careful aiming) and are quite lethal at the ranges of self defense (7 yards is a long shot in the house). My 2 cents.
PS
I have an Ithaca Model 37 lightweight with the old straight cylinder choke smooth bore barrel that was their Foster slug barrel predating rifling. It has a wide pattern with shot, already opening up at 7 yards so it has a pattern diameter of several inches (about 6 or so) vs the tight pattern of about a 3 inch diameter offered by my full choked Browning A5 at that range. This is my self defense firearm.