whelennut... I did not and do not have space and time to go over all the nuances of the ballistics tests I reported on, let alone all the ballistics tests I've viewed, reviewed, and discussed with professionals far more expert than I.
But in answer to your question re: 9mm vs 45 ACP. First, I'm not saying they are ballistically equivalent, as they're obviously not. The 9mm, being a lighter, narrower projectile, has to "work a lot harder" to produce the same effect as a 45 ACP. And a 45 ACP bullet has to "work a lot less hard" to produce the same effect as the best 9mm round. But in simple terms, yes, a Speer GDHP or Winchester Ranger Talon or Federal HST 9mm bullet will penetrate as far in gelatin as a 45 ACP bullet of the same groups, and will expand as reliably. The kinetic energy transferred will be close to the same. The only significant difference will be the size of the permanent wound cavity, and even then it's not a large difference (about 20% more surface area with the 45).
The performance difference between 380 ACP (9x17) and 9mm Luger (9x19) is not something I can explain. I am not a physicist. The 380 case is significantly smaller, with smaller powder capacity. Its narrower diameter means it pushes pressures higher and faster than a wider, longer case such as the 9mm so its "+P" potential is really limited. From what ballisticians tell me, the 9x19mm case is really about as small as you can go to produce acceptable service caliber ballistic performance.
The plain fact is that all service caliber handgun bullets are pretty anemic when compared to rifle or shotgun rounds, and the "heavy" handgun rounds (44 Mag and up) as used in police shootings haven't really performed at a level to inspire enough confidence to use them rather than a patrol rifle.
Let me put it as plainly as I can: I've seen enough blocks of gelatin shot, and enough ER cases and autopsies, to be fairly confident that the "stopping power" of good-quality handgun ammunition in 38 Special, 9mm Luger, 40 S&W, and 45 ACP is all about the same. If I was issued a 9mm service handgun and told to make do, I am confident it would do the job provided I placed my shots correctly. If given a 45 ACP handgun, same deal. But if I was issued a handgun outside of these calibers, on the lighter side anyway, I'd have grave doubts as to my career longevity with that agency.
