I can't imagine that makes no difference in stopping power, all else being equal.
Imagination isn't really necessary. If you want to measure the physical difference between a .45 caliber projectile and a 9mm projectile permanent cavity, the best measurement is of the surface area of the wound track. I've done some of this research myself, and it's insanely difficult. I've also collaborated with one of the foremost wound ballistics researchers in the world. But for what it's worth, to the best of our estimation, the difference in surface area of the permanent cavity between 9mm and 45 Auto is about 20%. That's it. It's not physiologically or anatomically significant. All other ballistics factors are roughly equal as well.
Although there is a lot of anecdotal "evidence" offered by people based on their personal experience in the medical/paramedical field, there really isn't any generally accepted peer-reviewed publication to establish one service caliber being superior to another. (By definition of "service caliber", the wound ballistics literature includes the common LE/Military rounds in use in the USA: 38 Special, 357 Magnum, 9mm, 357 SIG, 40 S&W, 45 ACP. Other calibers such as 10mm, 41 Magnum, 44 Special, and 44 Magnum are in sporadic use by isolated agencies and are not generally included in comparative studies. Sub-optimal calibers such as 380 Auto, 32 Auto, and 22LR do not perform at a level, either in the lab or on the street, to qualify for duty carry. This doesn't mean they can't be highly effective manstoppers if used well, it just means arming your cops with such guns is an invitation to a lawsuit, so nobody issues them for duty.)
Ed Sanow (of Marshall & Sanow fame) continues to collect data according to the established Marshall & Sanow method. I attended a talk he gave at the ILEETA convention a couple of years ago that updated the data listed in their two published books. These data didn't really tell us anything new, but rather confirmed that the standard service calibers, when loaded with reliable hollow-point ammunition, are all pretty capable of stopping a human being from offering further violence.
I teach wound ballistics and shot placement to LE agencies all over the USA and Canada. As such, I am privy to details of a lot of shootings. My accumulated files over the past decade or so confirms pretty much what the established researchers have been saying for years, i.e., that
what you shoot 'em with (as long as it's one of the service calibers described above) is far less important than
where you shoot them.
Agencies that train their officers to shoot the most vulnerable anatomic regions of the body have a much higher rate of "successful stops" than agencies that don't teach this targeting method,
regardless of caliber.
The important lesson to draw from this is that worrying about gun/caliber is far less important than selecting a gun in one of the service calibers that you can shoot well, and then to train with it to the point of mastery. If the SHTF and you end up getting into a deadly force situation, any of the common calibers will get the job done as long as you are able to put your shots where they need to go.
