We are inundated with the message(s) that bullet expansion is a very critical factor in the performance of a bullet. But is it really?
Let's begin by considering this: Recall the FBI-Miami shootout. One of the very early shots from a 9mm that hit Platt was lethal, but unfortunately, it wasn't lethal quickly enough and Platt lived long enough to shoot and kill several FBI agents. Here's an analysis of that wound:
"...According to Dr. Anderson, the bullet passed under the bone, through the deltoid, triceps and teres major muscles, and severed the brachial arteries and veins. The bullet exited the inner side of his upper arm near the armpit, penetrated his chest between the fifth and sixth ribs, and passed almost completely through the right lung before stopping. The bullet came to a rest about an inch short of penetrating the wall of the heart.
In all of the discussions about this particular wound, not once have I read the first comment about the effectiveness of the bullet due to expansion. The one thing that was brought out was the lack of penetration. E.g. suppose, instead of the bullet coming to a rest, "...an inch short of penetrating the wall of the heart...", it had gone all the way through the heart? The entire outcome of the fight would likely have been dramatically altered.
Then consider this: A while back I started a thread titled, "Is there any real evidence that one caliber is a better fight stopper than another?" After a very long and very civil discussion, the only evidence presented was the very contraversial Marshal and Sanow study. The conclusion of the thread, I believe, was that there is little evidence that caliber is significant. I know we all have our personal opinions, etc. but after an enormous response, actual viable evidence was totally missing. Now I said that to say this...
Let's say a .32 magnum expands to .45" - you can see where this is going can't you? Is an expanded .32 magnum more effective than .45 ball? Don't they make the same size wound channel?
We can take this to the 'major' rounds, e.g. the same example with an expanding 9mm round and .45 ball. In this case, it is likely that an expanding 9mm round would wind up larger than a .45 ball. This is where it relates back to the "Is there any real evidence that one caliber is a better fight stopper than another?" Let's face it, essentially, caliber is nothing more than a definition of bullet size, esp. diameter and an expanding bullet increases the size or effective caliber. But in the discussion thread referenced, we concluded that caliber was essentially a non-issue, or at least there was no substantial evidence that indicated otherwise.
Some may say that there's a growing trend in LE to migrate to the .45ACP. But I know of some LE agencies that have gone back to 9mm.
Anyway, I'll leave you with this question: Is an expanded bullet more effective than an unexpanded bullet with the same effective diameters?