they have the same recoil and momentum, but the first does not expand/mushroom/enlarge as is passes thru flesh. The old military load has just 330 ft lbs of “striking force”, while the really hi-velocity load has 1000 ft lbs (foot pounds) of energy and animal tests prove that such a bullet is highly destructive to tissue and creates massive amounts of shock. That is IF that bullet is designed and made properly (which is almost never seen). When you have to stop a lethal attack, which would you rather have in your pistol? Old belief systems say that the lighter bullet wont penetrate adequately, but animal tests disprove that, too. One of the reasons that the 2300 fps (feet per second, about 1600 mph) is not commercially available is that it shoots thru Kevlar vests. It’s made of solid copper. 2 States, ILL and CA, require that handgun bullets have a "lead core’, but no size or weight of that ‘core’ is specified by law. So a tiny lead birdshot, in a hollowbase cavity, would make such an otherwise solid copper bullet conform to such laws.
Is there a debate topic in there somewhere?
Were you trying to ask a General Question with a factual answer? Or proposing a discussion with opposing sides?
If it is the former, I will move it to General Questions if you can clarify the question.
If it is the latter, I will leave it here if you can clarify the debate.
Failing that, I will shut down this thread.
[ /Moderating ]
here, so that they understand that this is a debate. Maybe they’ve got something that I’ve overlooked?
I’ll take “failing that” for 200, tom. 
I’ll take a shot at it, John (see what I…oh, never mind.) I hate this style of argumentation, FWIW, but it’s the only way I see to dig out the points of discussion from his wall of text. Like I should talk.
That’s true of both, from what you’ve told us
Please cite to the “animal tests” you’re referring to. AFAIK, the Strasbourg ‘goat tests’ didn’t evaluate such a projectile.
Yeah, I’m going to need a cite for that proposition too. Modern bullets are as well designed, as far as terminal ballistics are concerned, as they have ever been.
This is probably referring to the passage in 18 U.S.C. § 921 (a)(17)(b) which defines "armor-piercing ammunition (for the Federal Government, anyway). It states:
. There are some handgun bullets that have muzzle velocities in excess of 2300 FPS, and are not counted as armor-piercing. Plenty are exotic, true. The .460 S&W Magnum with 200 grain bullets (copper Barnes bullets at that) will touch that speed, depending on barrel length. It is not classified as an armor-piercing load, albeit this may be due to the specific cartridge being classified as having a “sporting purpose.” See, e.g., this note from the BATFE on how they determine whether a cartridge has a sporting purpose or not.
As to your last point, with regards to Illinois and California, I would look to whether they market handgun cartridges with Barnes copper bullets, and to whether those bullets meet those regulatory requirements.
Ironically, I’m probably on your side, OP, in as much as I am personally interested in the added terminal ballistics effects of projectiles over 22-2300 FPS on tissue, versus more typical handgun velocities. I suspect a synergistic effect between temporary wound cavities caused by projectiles at that speed, and fragmentation of such projectiles, leading to a much larger permanent wound cavity than would be expected by a mushrooming, expanding projectile. But I haven’t seen any evidence to prove that supposition. And entities like, e.g., Houston P.D. SWAT, that were one of the first LEO organizations to adopt the FN 5.7 PS90, a weapon that fires a high velocity small projectile like you’re talking about, but later stopped using it, make me think that the ‘small bullet/very high velocity’ paradigm just doesn’t work all that well in handguns/PDWs/SMGs. (But then CAG/DEVGRU supposedly love the HK with the 4.6mm, so what do I know?)
As to your two choices, I would choose “whichever one you can shoot most effectively.” Which is the typical way of weaseling out of the question. Handguns stop and kill by disrupting tissue, and in the words of the FBI when they looked at the question in the 1980s, they disrupt tissue via “the crush mechanism, the result of penetration and permanent cavity…the only [underlining in original] handgun wounding mechanism which damages tissue.” IOW, they poke a hole in the target.
You have to penetrate to vital tissues in order to either: disrupt the central nervous system—mess up their head or spine enough that their brain can’t send signals to their muscles to keep fighting OR drop their cranial blood pressure enough that their brain shuts down—either by poking enough holes in them that they lose enough blood so that happens, or by shredding their heart/major arteries enough that the pressure drops. And you can’t do either if your bullet shreds to pieces—as small high velocity projectiles are wont to do—before hitting those vital structures. Which are usually protected by bone (skulls, sternum), muscles/fat, limbs inconveniently in the way, or all of the above. So, I’d take the .45 hardball.
For this thread to remain in GD, somebody is going to have to post a screed in support of some 9mm krunchenticker loading at the Ultimate Manstopper™.
Well, I’m a fan of .50 caliber, 91 fps and green in color, personally.
Personally, I recall having read the reasoning that led to the development of the S&W .40 cal round. If I wanted a pistol for self-defense, that’s the way I’d go.
silenus, is that enough of a screed for you?
More opinion seeking than anything else.
Off to IMHO.