Definitions and terminology are key to understanding these issues...
What I understand about "shoot through", which is actually termed "penetration". That is the factor that deals with the round hitting, glancing or "going through" either human flesh, or natural substances like trees, brush, sand, rock etc etc...Or even man made products like building structures (i.e.: drywall, lumber, cinderblock, furniture, etc etc...)
A rounds' cross section doesn't have much to do with it unless it has a lot of force behind it...Of course a 9mm round has a smaller cross section to an object it hits, and they do have some substantial speed to the caliber...
A .45 being a larger caliber, sometimes sacrifices speed for energy into the target...Or what I have been told is called "force", and they measure that by foot pounds...
People I know also talk about how a .45 has plenty more "knockdown force" to a 9mm, which in some cases shoots a little flatter (the ballistic drop from the muzzle to the target is less than other heavier rounds)...
The velocity term you used is ok, but think of it more in terms of "energy"...
A rounds speed through the air downrange is not constant, factors like wind, barometric pressure, temperature and of course gravity all play on that round as soon as it leaves the barrel...
But I guess the bottom line to all of this is you are not going to be in any firefights with your defensive pistol, more than 25-30 feet if your lucky...
Why do you think they only want you to shoot at 15 yards on your CHL qualifier??? And not further...Of course practically this is not an absolute...But more of a personal judgement call to shoot at any range or condition...
Bottom line is that you are just as shot/dead with a 9mm as you are with a .45, both can very well penetrate a target in certain conditions, both have good energy into the target, and can stop a threat when the need arises...
But I also think that at the moment you are defending yourself, penetration is not a deciding factor on whether you shoot or not...It should be understood before-hand, that there is a risk to life and property from over-penetration from just about any caliber you shoot...
Thats one of those basic safety rules of shooting you have to be aware of when you go shoot...
The dynamics of a defensive shoot are a bit more complicated than just being at the range and shooting at a paper target...
Why do we practice shooting at the center of mass???
Thats is to reduce the chance of penetration, and more important...missing...
Personally, I think I may have gotten off track here, and I hope I didn't confuse the issue...
Thats why I do not shoot 9mm...I will if I have to, and have manytimes...But for defensive purposes, I took into consideration concealability, weight, round capacity and functionality...And cost somewhat...
I only own two pistols I carry for defensive purposes...
(1) SigPro 2340; shoots .40
(1) Glock 23; shoots .40
The numbers and performance of the .40 caliber at the time made more sence to me than any other caliber...
I am though entertaining the purchase a .45 sometime soon...But that firearm will be for times I will not have to worry about concealing anything...
The final steve-ism would be this...
Get real good with what you feel best shooting for defensive purposes, and stick with it...Train like you fight, and fight to win...
I feel a little guilty like I am preaching to the choir with all this, but what the hell...I would want everyone to sing, and sing well if it were all up to me...
Good luck...
:P[/quote]