....as long as the expansion is controlled properly once it starts. And I think that's smarter than making a bullet that's harder to get started expanding.

Spot raises interesting points, and this discussion has had me thinking of something I observed while testing the .380 in Perma-Gel. The Speer .380 Gold Dot is engineered so that once it expands to about .44" the expansion all but stops. By allowing the bullet to expand to the right diameter, and no more than that, the engineers at Speer are controlling how deep the bullet goes. There is no doubt in my mind that is what they did in the info tpd223 posted where he said that the 115 gr. and 124 gr. Gold Dots penetrated to about the same depth, but the 115 gr. bullet was a little smaller in diameter. I've seen overwhelming evidence that Hornady's engineers are doing the same thing in .380.

A bullet's design, weight, and velocity must work in harmony for it to be optimally effective. That is what all of the best handgun cartridges have going for them. A great example would be the Remington 125 gr. .357 SJHP. It is, as far as fight stopping performance goes, optimal for caliber, right down to the bullet weight. Of course, one cannot ignore the human factor; not everyone will shoot their best with that load, so lighter loadings and/or different weights may be the best bet for certain individuals.