In any discussion such as this, there are always a few definites...
Physics.
A heavier bullet (more mass and momentum)will always penetrate better than a lighter one. That's why a .45 with a heavier bullet should penetrate clothing, bones, etc. better.
All else being the same, but the .45 ACP and the 9mm aren't the same. You know good and well that there's much more than bullet weight that equates to penetration. Even if we back 100 years to the first 9mm vs. .45 ACP debates, the 9mm has always had better barrier penetration than the .45 ACP; and that still holds true today with modern loads. With a 124 grain +P or a 147 grain 9mm both barrier and tissue penetration will be greater than a 230 grain .45 ACP (this is not to say the .45�s penetration is insufficient). Because the physics are not the same between the two rounds, the penetration nod actually goes to the 9mm. But honestly I don�t think the edge is enough to get excited about.
Assuming similar terminal performance, large diameter bullet will always make a larger hole than a smaller one. The 9mm has for sure been the subject of advances in bullet technology in the form of good expanding bullets, and assuming they work as designed, they would be better than any FMJ. But if they don't for whatever reason, you're still shooting a FMJ.
This one is interesting because what you say makes a whole lot of sense. But when I have spoken to surgeons who have treated bullet wounds, they said they can�t tell the difference in actual tissue damage. Yes on some measurable level the tissue destruction just HAS to be greater with the .45 ACP, but I don�t think it�s enough of a difference that it actually matters on a human being. HUGE changes in numbers from say 50 caliber to 70 caliber are very big changes on paper. But in the real world it�s .2 of an inch. Compare that in relation to the human body, I just don�t see where someone shot with a 9mm would know the difference between someone shot with a .45 ACP. It�s just like a .257 Roberts vs the .30-06 in the field. On paper there�s a big difference, but I�ve yet to see where the .30-06 did a job that the .257 couldn�t have done. My observations, I�ve never seen an animal act any different when squarely shot with most centerfire rifle cartridges no matter what common "deer" round it was (generally .243 - 30-06).
Dr. Martin Fackler a man who has done more work on the subject of bullet wounds than any of us could ever dream of, will tell you that most handgun cartridges produce the same results, and most rifle cartridges produce the same results. Even though when testing meaningful differences can be found in test mediums, when it comes to reviewing actual bullet wounds, he said on the operating table he couldn�t tell the difference between a FMJ or JHP round from a pistol, or a 7.62x39 vs a 5.56. (unless it was an extremity hit for the latter)
My observation of treating gun shot wounds for many years, patients tend to look the same when shot with handgun wounds; regardless of caliber, bullet choice, etc.
In fact, the ONLY observable difference comes quite predictably in where they are hit, and how many times they were hit.
In summary, my opinion is 45 ACP = more margin for error.
On paper that makes sense, in the real world I�ve yet to see where it matters.
To me here�s what matters.
1 � Have a gun
2 � It must be a reliable gun
3 � It must be of a sufficient power to do the job (and most common defensive cartridges are)
4 � You must be able to shoot it well (competent and safe)
5 � You must be confident in the ability of you and firearm
Whatever gun meets that criteria for you is just fine, whether it be a 9mm or a .44 magnum; if it meets those 5 (at a minimum), then you�re probably good to go
Everything after that is personal preference and splitting hairs IMO.
