Specifically witnessed...one...45acp Hydra Shok. Know details of several more by other officers using various .357, .38spl, .40 and 9mm rounds. It happens from time to time.
This having been said, NO handgun round can be counted on to put a human down instantly! The handgun is the shortest-range, least powerful and most difficult to shoot well of all small arms. The reason we carry a handgun is because we cannot always carry a "real" gun.
Beyond that, there are "physical" stops and there are "psychological" stops. To generate a non-voluntary instant physical stop, you must generally strike the "control center" or the "support structure" (skelekal). Sometimes this happens, but in a fast, close situation where targets are moving and/or using partial cover, light and shadow, etc., you may be damned thankful to get one good hit center-mass.
At this point, you are looking at a "hydraulic" shot...and are dependant upon loss of blood (or blood pressure) to cause your opponent to stop trying to do bad things to you. Even if you get a center hit on the "pump", the "lines" are still pressurized and it will be several seconds before a determined (or doped-up...or both) opponent becomes involuntarily stopped.
Any idea what you can do in, say, 8-10sec. with a decent weapon? Any idea just how looonnng 10sec can be with someone shooting at you or trying to carve your guts out with a knife?
Make plans for your pistola to NOT work immediately...think about movement, barriers, cover. Think multiple hits...Hell, think multiple adversaries with multiple hits! Think of the pistol as a "hole punch"...big holes work better than small ones...more holes work better than fewer ones...deep holes work better than shallow ones...but best of all is a big, deep hole in the correct place.