Please explain , with all things being equal , including shot placement, any instance where smaller caliber handgun ammunition produces more effect than larger. Not talking about exotic stuff traveling at rifle velocity either. Let's keep it to .22, .380, 9mm, .40, .45 acp. Standard common ammo.
Hitting the exact same target in the exact same spot, what advantage does that .380 have over the .45acp?
All things are never equal and the differences are in the ability to hit the exact same spot with a heavier versus lighter recoiling cartridge/pistol combination, and in the number of hits that can be made in a given amount of time.
For example, I switched from .45 ACP to 9mm Luger for personal concealed carry when I played around with timed targets and realized that I could consistently score three A zone hits with a 1911 in 9mm Luger compared to just two A zone hits in the same amount of time with a 1911 in .45 ACP.
Less recoil made for faster follow up shots with the same degree of accuracy, and with advances in reliable 9mm hollow points making the switch made sense. Jeff Cooper is long gone, but I suspect if he were still around, he'd see the benefits in the overall speed, accuracy and power triangle with modern hollow points, as opposed to hardball ammo. He probably would not admit it, but he'd see it.
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Jeff Cooper hard ball comparisons and biases aside, it's true that a .45 ACP hollow point expanded to 1.5x original diameter will punch a hole with a cross sectional area 0.36 square inches compared to just 0.22 square inches for the 9mm Luger expanded to the same 1.5x original diameter.
Consequently, with two .45 ACP holes you have 0.72 square inches of frontal area. However with three 9mm holes you've got .66 square inches of frontal area. It's not a big difference, and the nod still goes to the .45 ACP until you consider wound cavity volume, since the 9mm Luger gives you three wound tracks rather than two.
Assuming instant expansion for comparison purposes and 15" penetration for both cartridges, those three slightly smaller 9mm Luger holes produce 29.7 cu in of wound track volume compared to just 21.6 cu in for two .45 ACP wound tracks. The 9mm Luger has a clear advantage.
You also have 10+1 capacity in a single stack 9mm 1911 compared to 8+1 in a .45 ACP 1911, and with a Hi Power or CZ 75, you have 15+1 capacity, which again equates to more shots in any given time frame, where more than 9 rounds are fired.
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Consider the .357 Mag versus the .41 Mag and .44 Mag. The .44
and .41 Magnums' recoil is severe enough that in police use both were loaded down - .44 Special and the equivalent of modern .40 S&W (200 gr at 1050 fps) in the case of the .41 Magnum police loads (210 grains at 1050 fps).
Even then, there are advantages in shooting a .357 Mag K frame compared to an N frame in .41 Mag or .44 Mag. For one, the N frame grip doesn't fit my hand.