What handguns do police use? Today, that really depends on the department...but there are a few dominant brands and models that tend to be the rule. 

Police duty weapons have evolved a long way not only over the 20th century, but especially in the last 20 years. 

Since the gun-buying public tends to mirror what police carry on duty, it's worth understanding what police carry on the job. 

Police Revolvers Of The 20th Century

Most of the 20th Century was dominated by the medium-frame double-action revolver, most of which were chambered in .38 Special. Colt and Smith & Wesson dominated the marketplace well into the 1970s, and were still commonly police issue duty weapons into the 1990s in many departments both here in the United States and abroad. 

In fact, it's not even uncommon to see police in some foreign countries still carrying them. 

The most common models were the Colt Police Positive , Smith & Wesson Model 10, and - to a lesser extent - the Colt Official Police. Standard features on all three models included six-shot cylinders and simple sights, often no more than a front sight blade and a notch cut into the top strap of the frame as the rear sight. 

The Colt Police Positive was introduced in 1907, it was an innovative design, featuring a new ‘Positive Lock’ safety feature that made accidental discharges virtually impossible. While also offered in .38 and .32 Colt, the most popular chambering was .38 Special. The Colt Official Police was almost identical, but had a slightly shorter cylinder as the Police Positive was designed to be able to chamber .32-20 as the caliber was (at the time) popular enough to offer it as a factory option. 

The Smith & Wesson Model 10 debuted originally in 1898 as the .38 Hand Ejector Model of 1899, the Model 10 quickly got the attention of police departments nationwide. Eventually, S&W's nomenclature would change and the Model 10 moniker would be adopted. Today's Model 10 is barely any different, except that it comes with a standard bull barrel. 

4- and 6-inch barrels were the norm, though 2-inch snubby models and eventually 3-inch round butt (the bottom edge of the grip frame is rounded) for concealment by plainclothes police would become popular as well.

Some police would carry large-frame revolvers, either in the rare cases where they were issued or as a personal auxiliary weapon. The Colt New Service (offered in .44-40, .44 Special and .45 Colt) and Smith & Wesson Hand Ejector (aka "Triple Lock") revolvers were the most common.   

The .357 Magnum cartridge was invented in the 1930s, but few police departments would adopt them until the 1950s as few agencies (and even fewer officers) could afford the steep price tag of the Model 27 or Model 28 Highway Patrolman (over $1000 inflation-adjusted) or Colt New Service. Medium-frame magnums would arrive with the Smith & Wesson Model 19, Colt Trooper and - for the officer who could afford one - the Colt Python. 

Smith and Wesson would later bolster its magnum service revolver offerings with the advent of the L-frame, a slightly larger medium frame with additional material to withstand constant magnum factory loads. The Model 19 was known for not being able to cope with a heavy diet of full-power .357, but the new L-frame Model 586 was purpose-built for it. 

Round-butt models for concealment such as the S&W Model 13 would also be popular in police service; the Model 13 was the standard service revolver of multiple departments as well as the FBI from 1981 to 1991. 

In the 1970s, Ruger emerged as a competitor with the Speed Six and Security Six revolvers, both in 4- and 6-inch service pistols and 3-inch round butt models, but even by then the writing was on the wall that semi-autos were going to replace them. 

Early Semi-Auto Police Pistols

Early police semi-auto use was mostly in urban departments. It was socially unwelcome for even police to open carry their duty weapons, so most police officers of the 19th century and much of the 20th century would conceal their duty guns in pocket or under a jacket. 

Early police semi-autos were compact medium-bore pistols like the Colt 1903 Pocket Hammerless (favored by the Boston Police Department and Shanghai Municipal Police, largely made up of British expats) and later the Walther PP series, which was created for the German police. 

Some departments would adopt or authorize civilian M1911 pistols, especially the 38 Super variants in the 1930s. While never popular for mainstream police use, the 1911 pistol would catch on in select police units (such as LAPD Swat, LAPD SIS, the FBI's Hostage Rescue Team and select FBI SWAT units) in the 1970s and 80s. The Commander model would also find some popularity in plainclothes use as well. 

One of the first semi-autos after the 1911 to see much police use was the Smith & Wesson autos. Early adopters included the Illinois State Patrol, who issued the Model 39 (a single-stack 9mm DA/SA pistol) and the Bakersfield Police Department, who adopted the Model 59 (same upper and barrel, double-stack magazine) when it came onto the civilian market in 1971. The second- and third-generation S&W autos like the 459, 5906, 1046, 456 and 4506, were also common police issue from the 1980s into the 2000s. 

The other brands to dominate the police market starting in the 1980s and into the 1990s were Glock, Sig Sauer and Beretta. The Glock 17, 22, 23 and 19 first gained acceptance in the US police market beginning in the early 1990s, which has grown to the point that Glock is now the single most-common police duty pistol. 

Starting with the FBI's adoption of the .40 S&W cartridge, much of the United States' domestic police force switched to this caliber. Almost all of the common police issue pistols of the day were chambered for it, and until fairly recently most pistols based on a 9mm frame-size would likewise be offered in that caliber. 

Sig Sauer's P220, P226 and P229 DA/SA pistols were common police issue for state and local departments as well as federal agencies like the FBI, Border Patrol and beyond, in fact remaining common into the early 00s. 

The Beretta M9/92FS pistol, another one of the high-capacity "Wonder Nines," was also a common police duty pistol (as well as the 96FS, chambered in .40 S&W) for the last quarter of the 20th Century as many officers had gained familiarity in military service. H&K managed to make some inroads into the law enforcement market with the USP series. 

Modern police duty pistols, however, are quite different. 

Modern Police Handguns

The modern police handgun is a full-size or compact polymer-framed striker-fired pistol, usually chambered in 9mm but with a few holdouts still clinging to .40 S&W. Almost no departments insist on .45 ACP anymore. 

The typical police pistol of today has - at minimum - night sights, if not a milled slide for accepting a red dot sight. The frame is railed for mounting a pistol light, usually a full-size light such as the Streamlight TLR-1, SureFire X300 or Modlite PL350. 

The Glock 17 and 19, as well as iterations such as the 19X, 45, 34, and now the Border Patrol's duty pistol, the Glock 47 are the most common, with the .40 caliber Glocks (22, 23) also still represented in the field. 

Smith and Wesson's new generation of duty pistols, the M&P series, is somewhat common with the M&P9 and M&P40 (both original and M2.0 versions) being far from uncommon in police use in the United States. 

Sig Sauer's P320 pistol made a splash as the new issue handgun of the US military (in M17/M18 guise) and has found some adoption in US (and foreign) departments as well. 

The LAPD decided to go in a different direction altogether, adopting a variant of the FN509 (itself an entrant in the US military trials) for standard issue. 

Common auxiiliary pistols include all of the above, but many departments will allow officers to supply their own gun. The Sig Sauer P220 series is commonly approved for duty use, as well as Berettas, and in more recent years, Staccato 2011 pistols as well. 

The modern duty gun is vastly different than what police officers had to use even as recently as 30 years ago.