Revolver

A revolver is a type of handgun distinguished from pistols by the presence of a revolving cylindrical chamber that holds cartridges.

History
Revolvers were first invented in the 1800s. Today, they have been widely replaced in military and law enforcement by semi-automatic handguns due to their larger ammo capacity and increased safety, among other features, but are still popular among civilians. Revolvers typically feature a cylinder with 5 or 6 chambers for bullets, although there are models with as many as 10 chambers, depending on their caliber.

Non-Criminal
The following non-criminal characters use/used Revolvers
 * Season Two
 * An Unnamed Deputy ("The Boogeyman") - He is seen wielding a Smith and Wesson Model 66.
 * Sherriff Georgia Davis ("No Way Out") - She is seen holding a Smith and Wesson Model 66.
 * Spencer Reid - Reid first used a Smith and Wesson Military and Police Model to shoot and kill Tobias Hankel. He also frequently uses other models throughout the series.
 * An Unnamed Man ("Fear and Loathing") - He uses a Colt Python to kill a cop and later hold Morgan at gunpoint.
 * Season Three
 * Unnamed Foster Child ("Children of the Dark") - He briefly wields a Astra 357.
 * Tina Lopez ("In Heat") - She briefly shows Morgan her Smith and Wesson 442 Airweight.
 * Season Nine
 * Penelope Garcia - She uses Reid's Smith and Wesson Model 65 in "Demons".

Criminals
The following criminals used Revolvers in their crimes
 * Season One
 * Maggie Lowe ("Somebody's Watching") - A serial-turned-spree killer, assassin, stalker who used a Harrington and Richardson Model 929.
 * Season Two
 * "The Hollow Man" ("The Last Word") - A serial killer who used a Smith and Wesson Model 29 to kill his victims, and later hold a man hostage.
 * Tobias Hankel ("The Big Game" and "Revelations") - A serial killer, hacker, one-time angel of death, and abductor who used a Smith and Wesson Military and Police Model to taunt and threaten Reid. Reid later used it to shoot and kill Tobias.
 * Season Three
 * Max Poole ("About Face") - A budding serial killer, budding serial rapist, stalker, and abductor who tried to shoot Rossi with .357 Magnum Smith and Wesson Model 28.
 * Henry Frost ("Identity") - A budding serial killer, attempted copycat, abductor, and accomplice of Francis Goehring who used a Smith and Wesson Model 13.
 * Jason Clark Battle ("Lucky" and "Penelope") - A serial-turned-budding spree killer, stalker, and one-time cop killer who used a Smith and Wesson Model 36 to shoot Garcia after their date. He also purchased a Smith and Wesson model 67 earlier.
 * Season Four
 * Chloe Kelcher ("The Angel Maker") - A serial killer, budding serial rapist, copycat of Cortland Bryce Ryan, necrophiliac, and one-time cop killer who killed Sid Rutledge using a Smith and Wesson Model 36. She later used it in an attempt to kill Merrill Dobson.
 * "Animal" ("Brothers in Arms") - A one-time stalker and serial-turned-spree killer and cop killer who used a .357 Magnum Smith and Wesson Model 66.
 * George Foyet ("Omnivore", "To Hell and Back, Part 2", and "100") - A prolific serial killer, hebephile, brief spree killer, one-time mass murderer, stalker, and one-time cop killer who used two revolvers: a Smith and Wesson Model 629 Performance Center and a Smith and Wesson J-Frame. He also appeared in Season Five. He also appeared in a hallucination using a Colt Python in the Season Six episode "Route 66".
 * Season Five
 * Patrick Meyers ("Nameless, Faceless") - A spree killer and stalker who used a Smith and Wesson Model 10.
 * Wade Hatchett ("Solitary Man") - A highway serial-turned-spree killer and abductor, who briefly held a Smith and Wesson Model 19 Snub Nose.
 * Ronald Boyd ("A Rite of Passage") - A prolific serial-turned-spree killer, copycat, cop killer, one-time mass murderer, and one-time enucleator who draws a Smith and Wesson Model 36.
 * Billy Flynn ("Our Darkest Hour" and "The Longest Night") - A prolific serial-turned spree killer, serial rapist, abductor, robber, and one-time cop killer who used a Smith and Wesson Model 19 Snub Nose. He also appeared in Season Six.
 * Season Six
 * Sydney Manning ("The Thirteenth Step") - A spree killer, thrill killer, arsonist, and robber who used two revolvers in her killing spree with Raymond Donovan. The exact model is never specified.
 * Lucy ("Supply and Demand") - A killer, abductor, human trafficker, and proxy killer who threatened Renee Matlin with a Smith and Wesson Model 60.
 * Shelley Chamberlain ("Hanley Waters") - A spree killer, one-time mass murderer, one-time cop killer, and one-time robber who used a Smith and Wesson Model 64 Snub Nose.
 * Season Seven
 * Regina Lampert ("Unknown Subject") - An abductor and attempted murderer who held Hamilton Bartholomew at gunpoint with a Ruger SP101.
 * Season Eight
 * Arthur Rykov ("Through the Looking Glass") - A serial killer, family annihilator, stalker, and abductor who attempted to force one of his victims to shoot another with a Smith and Wesson Model 10.
 * Season Thirteen
 * Jeffrey Whitfield ("Neon Terror") - A serial-turned-spree killer, one-time robber, stalker, and copycat who shot his victims with a Smith and Wesson Model 29.

Model 10
Model 19
 * Cartridge: .38 Special
 * Capacity: 6 Rounds
 * Barrel Length: 2", 2.5", 3", 4", 5", 6" (as of 2007 only produced in 4")
 * Fire Modes: Double Action
 * Frame: K-frame (medium large)
 * Material / Finish: Carbon Steel / Blue Steel, Nickel
 * Cartridge: .357 Magnum
 * Capacity: 6 Rounds
 * Barrel Length: 2.5", 4", 6"
 * Fire Modes: Double Action
 * Frame: K-frame (medium large)
 * Material / Finish: Carbon Steel / Blue Steel, Nickel

Model 28

 * Cartridge: .357 Magnum
 * Capacity: 6 Rounds
 * Barrel Length: 4", 6", 8.375" (8⅜)
 * Fire Modes: Double Action
 * Frame: N-frame (large)

Model 29

 * Cartridge: .44 Magnum / Special
 * Capacity: 6 Rounds
 * Barrel Length: 4", 6", 8.375" (8⅜), 10.625" (10⅝)
 * Fire Modes: Double Action
 * Frame: N-frame (large)
 * Material / Finish: Carbon Steel / Blue Steel, Nickel

Model 629

 * Cartridge: 44 Magnum / Special
 * Capacity: 6 Rounds
 * Barrel Length: 4", 6", 8.375" (8⅜), 10.625" (10⅝)
 * Fire Modes: Double Action
 * Frame: N-frame (large)
 * Material / Finish: Carbon Steel / Stainless Steel
 * Notes: variation of the Model 29, differs only in the finish (stainless steel)

Model 36

 * Cartridge: .38 Special
 * Capacity: 5 Rounds
 * Barrel Length: 1.875" (1⅞), 3"
 * Fire Modes: Double Action
 * Frame: J-Frame (small)
 * Material / Finish: Carbon Steel / Blue Steel, Nickel

Model 442

 * Cartridge: .38 Special
 * Capacity: 5 Rounds
 * Barrel Length: 1.875" (1⅞), 3"
 * Fire Modes: Double Action
 * Frame: J-Frame (small)
 * Material / Finish: Aluminium / Blue, Matte Black

Model 60

 * Cartridge: .38 Special / .357 Magnum
 * Capacity: 5 Rounds
 * Barrel Length: 1.875" (1⅞), 2.125", 3", 5"
 * Fire Modes: Double Action

Model 64

 * Cartridge: .38 Special
 * Capacity: 6 Rounds
 * Barrel Length: Varied
 * Fire Modes: Double Action
 * Frame: L-frame (medium)
 * Material / Finish: Stainless Steel
 * Notes: Stainless Steel variant of Model 10

Model 65

 * Cartridge: .357 Magnum
 * Capacity: 6 Rounds
 * Barrel Length: 3", 4"
 * Fire Modes: Double Action
 * Frame: K-Frame (medium large); replacement parts L-frame (medium)
 * Material / Finish: Stainless Steel
 * Notes: Stainless Steel variant of Model 13

Model 66

 * Cartridge: .357 Magnum
 * Capacity: 6 Rounds
 * Barrel Length: 2.5", 3", 4", 6"
 * Fire Modes: Single Shot (Double Action)
 * Frame: K-frame (medium large)
 * Material / Finish: Carbon Steel / Stainless Steel
 * Notes: Variant of Model 19; differing only in finish (stainless steel)

Model 67

 * Cartridge: .38 Special
 * Capacity: 6 Rounds
 * Barrel Length: 4" (standard)
 * Fire Modes: Double Action
 * Material / Finish: Blued Carbon Steel w/ sandblasting and serrations
 * Notes: Variant of Model 15

Official Police

 * Cartridge: .38 Special
 * Capacity: 6 Rounds
 * Barrel Length: 4", 5", 6"
 * Fire Modes: Double Action
 * Frame: E-Frame (medium)
 * Material / Finish: Carbon Steel / Blue Steel, Nickel

Python

 * Cartridge: .357 Magnum
 * Capacity: 6 Rounds
 * Barrel Length: 2.5", 3", 4", 6", 8"
 * Fire Modes: Double Action

Ruger SP-101

 * Cartridge: .22 LR / .38 Special / .357 Magnum / .327 Federal Magnum / 9mm / .32 H&R Magnum
 * Capacity:
 * 5 Rounds (.38 Special, .357 Magnum, 9mm)
 * 6 Rounds (.327 Federal Magnum, .32 H&R Magnum)
 * 8 Rounds (.22 LR)
 * Barrel Length: 2.25", 3.06", 4.2"
 * Fire Modes: Double Action
 * Material / Finish: Stainless Steel

Harrington & Richardson Model 929

 * Cartridge: .22 LR
 * Capacity: 9 Rounds
 * Material / Finish: Blued finish

Charter Arms Bulldog

 * Cartridge: .44 Special / .357 Magnum
 * Capacity: 5 Rounds
 * Barrel Length: 2.2", 2.5"
 * Fire Modes: Double Action