Actually, physisologically, 3 cubic inches isn't really all that significant, unless it's 3 cubic inches of heart muscle or brain tissue.
"You can beat the drum until it breaks, but 9mm has always been, and will probably remain, viewed as more marginal, even for a pistol defense round, than the bigger bore ones."
The funny thing about it is, it's really not so much the 9mm people beating the drums as some of the .45 people coming swooping down like the screaming meemees over what most often are only perceived insults.
The .357 Mag. round certainly isn't viewed as being a marginal round. Yet it's nominally a 9mm bullet, and some of the 9mm loads available are pretty close ballistic matches to highly regarded .357 Mag. loads. Curious.
Take your pick, Fackler's jello junkies or even Marshall & Sanow's one-shot-stop crapola. Both agree that the 9mm with modern bullets and .45s with modern bullets show performance levels amazingly similar.
Then we have this...
"Some dudes also allegedly shot up some mean French goats and said the same thing--"9mm equals .45ACP!"
You know, it's been a long time since I read the reports on the supposed goat tests, but I don't remember getting that at all.
I do remember getting the supposed fact that the Glaser was supposed to be the best performing bullet in all calibers over .380, and the results were fairly mixed.
That is, if you believe the goat tests ever took place. I'm still out on the subject.
Now, if you go back to FBI tests in the 1980s, and the reasons why the 10mm and the .40 came about, in large part it's because both the .45 and the 9mm failed the early batches of tests that FBI designed, and failed them pretty miserably.
That's right, they both failed.
Largely due to the bullets that were then available.
Now we need to look at this...
"The trend has been a distinct migration away from the 9mm despite all of this ballistic equivalency, nay outright advantages it allegedly has over the .40-.45 pistols replacing them."
In order to understand that properly, one has to understand the contextual timeline.
It looks pretty convincing, on its face. But if you understand what was going on at the time, you'll finally begin to understand that appearances can be very very deceiving.
Timeline...
Early 1980s. The "Wonder9" craze starts, drug wars start breaking out, police everywhere feel that they're outgunned, and the mad rush from revolvers to 9mm semi-automatics begins.
1986 (IIRC). Miami shootout. Despite the piss poor tactics and preparation of the FBI agents involved, which result in several of them being killed or gravely wounded, the blame for the entire situation isn't placed on the men involved, it focuses almost squarely on a single 9mm Winchester Silvertip bullet.
That Silvertip bullet, despite actually showing good penetration and almost textbook expansion, is pilloried as the reason the FBI screwed up.
Police agencies all over the nation pause in their tracks, wondering if they did the right thing in adopting the 9mm.
Later 1980s. Glock is quickly winning the lion's share of police handgun sales in the nation with their 9mm 17s and 19s.
FBI begins testing possible successors to the 9mm Winchester Silvertip, including the .45 ACP and a variety of rounds, and finds that most all of them fail to one degree or another in the test procedures that they've laid out.
FBI allows its agents to carry either a 9mm OR a .357 Magnum, as they see fit, during this period.
Very late 1980s, early 1990s. FBI adopts a 10mm pistol despite many reservations. After numerous problems in testing, they load the round down to the 10mm Lite. The new bullet designed for it, however, shows very good performance in the FBI's tests, including a variety of penetration scenarios.
At the same time, S&W begins working on the .40 S&W, essentially the 10mm FBI reound in a cut down case. It is masterfully marketed, essentially as the second coming of Christ.
When the round is released in late 1989, it already has huge popular support, based largely on supposition, and police forces that went to the 9mm in the early 1990 now start to move to the .40.
Early 1990s. Based on the FBI's testing, bullet manufacturers begin to move designs into the computer age. New designs offer VASTLY superior performance. Dr. Martin Fackler laid out his criteria for what a bullet should do, and the manufacturers responded.
Early 1990s. The initial batches of .40 caliber ammo didn't have these new bullets, and California departments report several rather frightening failures of the round to do the job, based almost solely on bullet performance.
Late early 1990s and up to today. The new generation of bullets in all calibers has shown what the proper application of computers can do for ballistics. With properly designed bullets, performance in all calibers used in police work show amazingly similar results and efficacy.
And all through the 1990s?
The move away from the 9mm that began after Miami began to slow, and numbers of departments that use 9mm vs .40 vs .45 has stabilized.
There are still something like 100,000 police officers in the United States that use the 9mm, and have good results with the round as long as the proper ammunition is selected.