I originally wrote the following back in 2011 regarding a similar thread. My opinion on things hasn't changed materially.
The police duty weapon is used the vast majority of the time as a tool of psychological intimidation. Its presence both holstered and drawn serves to remind the criminal element that we are capable of responding to their actions to the point of causing their deaths. When drawn it serves to immediately underscore the point that we are engaged in serious business. Criminals over the years have learned the majority of the situations when we are unlikely to shoot them and frequently make their observation of the situation known. "Don't do me like my boy [insert name of most recent subject the police have shot]. I know all you pigs like to shoot [insert race and gender of suspect]." Conversely if the subject is of the belief that they may actually be shot, and have made the decision to not engage in any resistance their statements usually is much different: "Don’t kill me! Don't kill me! Don't kill me!"
The majority of the public, the criminal element included, gather their knowledge of firearms from movies and television shows. Reality television and the internet have to an extent given the public a slightly more accurate view of a hand guns effects on someone, but there are still hundreds of Hollywood shootings that show someone flying backwards through the air from a 9mm impact. Suspects frequently have perceptions of a weapons effectiveness based on what they have observed in the media. A 9mm will bounce off ones chest, where a .45 will blow your arm off. A shotgun will simply saw a man in half. Perhaps one of the single most recognizable handguns in the media is the .44 magnum revolver. Specifically the S&W model 29. The character of Inspector "Dirty" Harry Callahan immortalized it in several films, and the phrase: "it'll blow a man’s head clean off," and "do you feel lucky punk,” have been indelibly inked on several generations.
A 6” revolver invariably causes everyone (even cops) to quote Clint Eastwood. Most anyone who has a pistol pointed at them has a very distinct difficultly in accurately describing the bore. Comments of "as big as a cannon” or simply "huge" are common. The psychological shocking effect of a 6" nickel revolver is massive compared to that of say a Glock. The public, and the criminal element, have been socialized to believe that all large shiny revolvers are .44 magnums that "will blow a man’s head clean off." This psychological shocking affect is something that can not be overlooked when discussing police arms.
A modern 7 or 8 shot revolver shooting a service cartridge (.38 spl +P, .357 mag, 9mm, .40 S&W, .45 ACP, even .41 and .44 magnum) is no less ballisticly efficient then their auto loading counterpoints. The decrease in ammo capacity is not as dramatic, when viewed against single stack magazine pistols. The 1911 is considered one of the holy grails of fighting pistols, and it has the same magazine capacity of an 8 shot revolver.
For the officer that is willing to devote the time and effort to master shooting a revolver they have few disadvantages even when compared to the modern service semi-auto pistol. Reloading a revolver, even with moon clips, is a more fine motor skill intensive issue then reloading a semi-auto pistol. The revolver is normally larger and heavier than a comparable semi-auto pistol; however none are so large as to preclude carrying on duty.
Personally I don't feel the least bit under gunned with my G34 in 9mm w/ 52 rounds available, and I wouldn't feel under gunned with a 686+ and 21 rounds of .357 mag.
-Jenrick
( and from 12 gauge to ar's 
