The new conventional wisdom is that the selection of handgun c̶a̶l̶i̶b̶e̶r̶ cartridges doesn't matter, as long as it is at least 9x19 mm and - well - conventional. Or, one of those newfangled .380 ACPs with "modern" hollowpoints - er, something.
Apparently, modern "quality" "defensive" ammunition is so great that all "major" run-of-the-mill cartridges will save your life. Oh, and shot placement is "now" the most important thing. But high pressure cartridges apparently beat up guns, and heavier bullets risk over penetration. But again, having one of the regular players levels the field.
So, I sit comfortably with my selection of the 9mm "for war" cartridge in a handgun that can handle +P, NATO, and +P+ - I guess. And as a disclaimer, my chances of getting in a gunfight are irrationally south of nil. But people love to parse differences, so ...
TO BE CONTINUED