so, if one could shoot the .45 as accurate as the 9mm,
then the .45 would be better.   

what does it mean when the 9mm round is referred to as "legally defensible?"

With modern ammunition, the difference in performance is getting pretty marginal. In theory, the large .45 should create a larger permanent wound channel.

However, look at the three ways to effective stop someone.

Destruction of the central nervous system, aka brain or spine shot.  Near instant incapacitation in almost every case.  Makes no difference between 9mm or .45.

Major organ failure.  Heart, lungs... something that should be working suddenly isn't.  A 9mm or .45 in the right spot will do the same thing.  The temporary wound channel/expansion for either round is significant.

Fatal blood loss.  Probably the only time where the extra size of the .45 would be a clear advantage.  However, it really depends on how many holes, and how close to a major artery you hit.

So in general... accuracy and multiple hits is more important than caliber in most of the aspects.  I love my .45, but I bought it when .45acp was only a few dollars more a box than 9mm.  Now 9mm is between 1/2-2/3rds the price of .45acp on any given day.  Cheaper ammo means more range time. More range time is always a good thing.

Yep.  Switches and timers.  Another thing to consider is that if you don't hit the switch, the aggressor/threat will likely be on top of you, even if you get multiple hits on the center of mass.  I'd have to look up the studies, but IIRC, something like an average of about 15-20 seconds of aerobic capacity left even if someone is hit where they will eventually bleed out.  The point is that you should plan on having to deal with the aggressor "up close and personal" even if you are able to shoot him center of mass.

so, if one could shoot the .45 as accurate as the 9mm,
then the .45 would be better.   

If you also can afford to shoot .45 ACP. . . then you can buy beers for the rest of us too! 

Yep.  Switches and timers.  Another thing to consider is that if you don't hit the switch, the aggressor/threat will likely be on top of you, even if you get multiple hits on the center of mass.  I'd have to look up the studies, but IIRC, something like an average of about 15-20 seconds of aerobic capacity left even if someone is hit where they will eventually bleed out.  The point is that you should plan on having to deal with the aggressor "up close and personal" even if you are able to shoot him center of mass.
 

If you also can afford to shoot .45 ACP. . . then you can buy beers for the rest of us too! 

Hell, there are cases of guys taking shots to the heart that keep going for another 20-30 seconds.  Adrenaline, drugs, physiology, and plain damn stubbornness to die are all things will play an X factor.  That's why the concept of "one shot stop" is a joke.

Hell, there are cases of guys taking shots to the heart that keep going for another 20-30 seconds.  Adrenaline, drugs, physiology, and plain damn stubbornness to die are all things will play an X factor.  That's why the concept of "one shot stop" is a joke.

Yup.  Maybe even more.  I just remember the 20 second figure for some reason.  I think it was because in a class, the instructor said something like "guess how much time it will take for me to close XXX distance".  It was probably something like 30 feet and we were amazed that even guys in moderate shape could close that distance in just a few seconds.  Which meant that they have at least 15+ seconds where they'll be on you, engaging you and if they have a knife, they are probably cutting you! 

Drugs seem to be increasing in prevalence as well.  I remember that line from Black Hawk Down where the Colonel mentions that they'l be hitting the market in the afternoon when the Somalis are "all hopped up on cot".  Not "exactly" the situation that any of use would likely face, but that amphetamines do give people seemingly super human powers. 

That "one shot stop" sure is pretty effective for the movies though!   

If you also can afford to shoot .45 ACP. . . then you can buy beers for the rest of us too! 

sure.
the Colt 45 is on me!   

Didn't take long for this to devolve into a 9mm vs 45 thread.

I have to blame this one on macsak. If you read my first post you'll see I was being quite neutral.
Mac encouraged me, or perhaps harangued is a better term, into espousing the obvious superiority of .45 ACP over puny, insignificant 9mm.

I'm really the innocent, injured party here.   

In my opinion SD is anything you can grab before the perp gets you. If all you got is a 22, use it. I doubt anyone wants to get shot with that either. As for recoil control I doubt anyone would be rock steady in a situation like that. I believe the average shots for home defense is around two so I wouldn't even factor in recoil control unless you shooting something like a 500 S&W. I say pick what is affordable, what feels the most comfortable, and what you had the most training with. Size shouldn't matter but that's not what my wife says. 

Thanks for all the info.  Like I said I have a .45 so that's covered.  I was just curious how you all thought about 9MM for SD, and got some insight.  Awesome. 

I have to blame this one on macsak. If you read my first post you'll see I was being quite neutral.
Mac encouraged me, or perhaps harangued is a better term, into espousing the obvious superiority of .45 ACP over puny, insignificant 9mm.

I'm really the innocent, injured party here.   

yes
i am responsible, you are not
i make you wear that t-shirt all the time too