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@flab are you suggesting a .45 acp has less penetration than a 9mm?
@flab Do you have any experimental sources for that? The significantly higher energy woukd seem to offset that, but im only speculating.
You want a certain amount of penetration, enough to inflict a good wound channel, but *too* much poses a danger to anything behind your target. In a perfect scenario, the round penetrates your target completely and not one inch further. A higher speed, narrower projectile is more likely to go beyond that point than a broader one, regardless of total energy.
@flab well no, if we are talking theory then its a bit more complicated than that...
More velocity for the same weight projectile will obviously be more penetrating, but thats because it has more energy. But a higher velocity projectile at the same energy (so lighter) will be less penetrating. A 9mm is faster but has less energy thus shoukd be less penetrating in theory.
Let me try to find some ballistic gel tests on this to see if i can find a good real world answer though. Theory isnt always correct.
Ok so watched a few videos and, as expected, the actual answer is nuanced.
When shooting ballistic gel with no MDF, and using a FMJ bullet, then the 9mm indeed does have noticably more penetration. However if you are in a situation where you dont want deep penetration then you would be using hollow point...
When shooting hollow point on ballistic gel without MDF then 9mm and 0.45 ACP has exactly the same penetration. I t should be noted the 0.45 ACP while having the same penetration also did more damage to the gel in terms of cavity size... So in this particular test the .45 is superior as it has more stopping power for the same penetration.
When using MDF in front of the ballistic gel, however, we find the .45 ACP is significantly more penetrating than the 9mm.
so would seem that while the FMJ certainly gave results consistent with your claim, the more real world scenario of the hollow point in fact was counter to your claim and consistent with mine, that the ACP will be more penetrating than the 9mm.
Source for the hollow point tests:
@freemo the hands attached to these guns 
P.S : I live in Canada
@Clementulus When I traveled to Israel about 2 years ago at the border they asked "Do you have any weapons?"... I responded, while flexing "Just these guns!"... long story short they took me in the back and questioned me for like 3 hours before they let me in :)
@freemo hilarious. When I went in 2010 they pulled me aside and questioned me for 30 minutes because I was 20 cm shorter when my passport was made (they couldnt believe that I had grown that much in less than 2 years.)
@Clementulus yea their security is a bit insane even i thr best of circumstances.
@freemo
You need to have .380 on this list. Ruger LCP's are perfect for when one finds it unwise to carry a "real" gun. I have also seen some compelling evidence that says caliber isn't all that important when defending yourself from other human beings.
@IAmErik .380 and 0.40 both deserve to be on the list honestly. Sadly i was limited to 4, and these are the 4 that are my top picks so I went with it.
As for the importance of caliber... in most situations I'd tend to agree. Even a 0.22 is pretty deadly at close range, at least enough to incapacitate... But there is important differences like penetration potential which can be fairly critical when you consider other factors (like collateral damage).
