Availability [You have to have it with you.]
Reliability [It has to 'go bang.']
Penetration [It has to reach important bits.]
Placement [You have to hit important bits.]
If a bullet penetrates 18" without expanding, vs. a bullet that penetrates 9" with full expansion, which does more damage?
Ah, the eternal question....
For a .380, of which I have two. PPK/S, and P3AT, the up close BUG, has to just be reliable. Period. The Bad Guy in your face with a weapon in the supermarket parking lot, ATM, 7/11,, etc,...won't care.
Cor-Bon, Speer, Hornady, Rem. Golden Sabres, are all top shelf winners for JHP's, However, 5rds. of Magtech FMJ's at point blank range, even in .380, will change an attitude very quickly. (carry a reload)... Either way, .380 ammo has evolved, just like the .38 and 9mm. What was once considered a "marginal" caliber, is very adequate for SD, as long as it's reliable, and you focus on the target.
Here in the heat of S. Fl, my Kel-Tec, is just a habit of carry, with Speer Gold Dots. For its design and purpose, I never feel vulnerable, and damn sure won't be a victim. Some days, I carry a larger platform, but TEST your pistol with your choice.
BTW, don't keep your carry ammo for years, rotate it, shoot it, get another box. As my old instructor used to say: Inspect every carry round, rotate it to keep it fresh, maintain your mags, after all, you and your families lives may depend on it.
S