Matt - what is the minimum Taylor Factor (the formula you use) for defense cartridges? I can stack up energy numbers against your 9mm to show it's inferior to a .357sig, and then further the Sig is inferior to a .40 (Taylor factor), which itself is inferior to a 45, which is inferior to a .44mag... But we started with a 9oz pistol which is easily managed and ended up at a full frame revolver weighing nearly 3lbs with recoil said to be the maximum manageable limit for most shooters... All with 5 simple numbers...

The entire .380 vs 9mm, 9mm vs. 45, 45acp vs 44mag debate structure is flawed. You can always stack the cards to show the more powerful cartridge is more powerful...

What isn't readily told by these numbers, is the minimum requirement for killing the affected target. Nobody is surprised to be reminded a 9mm is more powerful than a .380 - but it's not really pertinent when a .380 is "enough".

Sometimes a bigger hammer is needed, sometimes a bigger hammer is just heavier and harder to swing.