Basically if I get attacked by a 200 lb guy and shoot him in the same spot, which cartridge will stop that attack faster? The question may in fact be moot as any common defense cartridge may work the same and at the same speed. But my point is that in the context of the OP's question, shot placement is not a correct or appropriate answer.
It's like if someone were to ask you "Which off road tires will give me the best performance in mud?" and people answer, "Gear ratio." It makes no sense because the question was about tires. Yes it's relevabt to off road driving, but it doesn't answer the question asked.
And don't forget the driver when talking about off-road performance. That's the factor that isn't addressed in
that analysis and the same human factor is almost always ignored in the gun caliber result analyses. Here's a link to a site addressing some of Jim Cirillo's suggestions. He died recently, but long retired and without losing a gunfight. His points argue against a lot of what we are taught about using a handgun in self-defense.
http://moderncombatandsurvival.com/featured/jim-cirillo-3-confessions-of-modern-day-gunfighter/ Much of his success was achieved using a J-frame S&W revolver -- but he carried several, so that reloading didn't slow him. No .40s or .45s for him.
There's no question that a BIGGER hole is better -- but that assumes that you haven't hit the central nervous system and your opponent is still able to fight back. If he's still able to function, even if he's dying,
he can still kill you.
When you look at results from the various studies available to us, you simply don't know whether a 9mm hit or .45 caliber hit is more effective based on those very generalized data sets: they tell us nothing, really, about the "driver," the context of the shooting (i.e., whether the bad guy was shooting back, the distance between the antagonists, the time of day, the proficiency of the shooters, or how long it took, etc.)
A lot of the available data is based on very small samples and the samples themselves were acquired using differing techniques. Why is that? Because there really aren't THAT many shootings in a given year, and even fewer that are given proper forensic analysis that is available to someone doing such a study. You
can look at gel tests, but ballistic gelatin isn't the same as human tissue that has a rib cage in front of it, that is covered with different layers of clothing, etc. Some such tests try to simulate a better human proxy -- but that is seldom mentioned in these discussions.
I'd argue that the only answer that is really relevant isn't really a caliber answer, but one that only YOU can provide. That question has two parts: 1) which round do you consistently shoot best, and 2) can you do so under pressure, when you're scared, maybe moving, and perhaps concerned about companions who must be pushed out of the way, given protection, etc.
Jim Cirillo thought one of the most important parts of readying yourself for a gun fight was FORCE ON FORCE training, even if it meant using those inexpensie airsoft pistols. (He preferred better tools.) An acquaintance who is a trainer with Special Ops troops at Ft. Bragg says these guy (many of who are Operators) use a lot of force-on-force sessions, with proper eye protection. I've seen this guy covered with tiny bruises from the rubber bullets fired from service weapons. (He said he freaked his doctor out once when he went to have his shoulder checked for a rotator cuff problem; the doctor saw all the bruises and was concerned his patient was having some sort of subtle blood/kidney/liver problems.)
Shoot the biggest caliber you shoot well, and practice. And hope you can find and keep your cool. Bigger
is better, IF you can hit something with that "bigger." But be honest enough to concede that "bigger" assumes that you're hoping to live long enough that the bad guy bleeds out or gives up the fight before you do.
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