THIS is why we have .40 S&W ammo today. After two FBI agent were killed in a gunfight in Miami, 1986, the FBI got serious about upgrading their firearms to something a little better than S&W revolvers loaded with .38+P and S&W Mod 459 9mm handguns. They did a LOT of study on the problem.
After the fight, all agents were allowed to carry the 9mm. And double action .45 S&W and Sig220s were also authorized, while the problem was worked.
They hit upon 10mm semi-auto, but thought the recoil a bit too severe to be be ideal. Dialed back, that 10mm becomes the .40 we have today. And why 10mm pistols were EVERYWHERE 20 years ago, but are hard to find now. Pistols in .40 are everywhere, and appear to be here to stay for a while.
It's why self-defense pistol ammo manufacturers test their ammo against FBI penetration standards. Because of this gunfight, there ARE standards.
I'm sure Jeff Cooper would (and probably DID) recommend .45ACP as the answer to the problem and specifically the single action 1911.
THIS gunfight is why your local cop has a semi-auto, often BIGGER than 9mm, on his belt instead of a .38, though.
We have better self-defense bullets now, but NOTHING is ideal. There is no magic bullet. No one brand is best. That doesn't mean you should go for budget ammo for self-defense. Go with a named brand is my recommendation. And be sure it works in your firearm.
Have a happy and honest Thanksgiving - Well, maybe not as honest as this ... *I want to disconnect myself from all this emotion. With alcohol.* Heh.
45 minutes ago