Marine Corps Rules of Gunfighting No. 26:  "Never attend a gunfight with a pistol whose first number does not begin with a "4".

 

That said, there are two considerations in the 9mm vs. .45 debate -- military issue rounds and those issued to law enforcement and avilable for use by civilians.

 

By various conventions, the Geneva and Hague Conventions, military ammuntion is restricted to full metal jacketed bullets to prevent "unnecessary suffering" to wounded combatants.  [The FMJ design is more to wound than kill because it takes usually four other people out of the fight to evacuate a wounded soldier and none for a dead one.]  Soft nose and hollow point ammuntion (as used for hunting game) is prohibited.  As orignially loaded by DWM at its adoption by the Germans in 1902, the 9mm Luger or Parabellum (now 9x19 NATO)  round was loaded with a steeply tapered bullet.  The bullet was designed to tumble upon impact and dump its energy into the target.  With the adoption of the Generva Convention shortly before WW1, the bullet was redesigned to use the infamous 115-grain FMJ projectile of today.  Bluntly, the 9mm in this loading is a very poor people "stopper".  When asked about the difference in calibers between the 9mm and the .45 auto at the time the Americans switched to the 9x19 NATO about 1982, an Israeli officer with much combat experience said: "Well the 9mm is an OK round.  You seldom need more than four hits to take the target down."  (As upposed to one with a .45 ACP.)

 

The European approach to their military pistol ammunition has been and continues to be: small caliber, light bullets, going at high velocity (1150 fps +).  The American approach has been: large caliber, heavy bullets, going at moderate speeds (about 830 fps).  Of the two, only the .45 ACP can be depended upon to take the fight out of a determined enemy with the standard military ball loading.  Our special operations troops and Marines have relearned this lesson on the battlefields of Afghanistan and Iraq.

 

Law enforcement and civilians are not bound by the Conventions.  They are free to use whatever kind of projectile will get the job done.  It is my preference to use the same idea with JHP and JSP bullets as the .45 ACP Ball round: a larger caliber (that you can control), a heavy bullet, and reduced speed.  Other folks like smaller and lighter bullets at higher speed.  The only way to be certain is to see what works for you and then use that. 

 

According to what I have read on the subject, the edge is given to calibers following the .45 ACP model (large, heavy slow) rather than the 9mm (small, light, fast).  Within the "one shot drop" category, the 230- grain Federal Hydra-Shok followed by the 200-grain CCI Lawman (aka "flying ashtray") bullets seem to work best.  The bullets for the .40 S&W would be the 180 grain Hydra-Shok; the .357 Magnum would be the 170 grain Hydra-Shok; the .38 Special would be the 158-grain Hydra-Shok; and the 9mm would be the 147-grain Hydra-Shok. 

 

I am not saying that other rounds will not work.  What I'm saying is the Federal Hydra-Shoks have produced very good results in real-world shootouts.  For me, I use what works.