B.A.U. (Behavior Analysis Unit) Chief SSA Aaron Hotchner (Thomas Gibson) carries a third-generation Glock 17 as his duty sidearm. A third-generation Glock 17 is also wielded by Dr. Spencer Reid (Matthew Gray Gubler) in the season's premiere episode "Mayhem" (S4E01). Season 4 marks the first time since the pilot that one of the members who previously carried a Glock discontinues doing so - in this case Reid, who only has his Glock 17 in "Mayhem", after-which he begins carrying a .357 Smith & Wesson Model 65 revolver. Other FBI agents and some police officers are seen with Glock 17 pistols.
Supervisory Special Agent Derek Morgan (Shemar Moore) carries a third-generation Glock 17 with a mounted Streamlight TLR-2 weaponlight/laser module as his duty sidearm.
SSA Emily Prentiss (Paget Brewster) uses a third-generation Glock 19 as her sidearm. Another Glock 19 (which appears to be an older second-generation variant) is used in "Roadkill" (S4E23) by Det. Quinn (Timothy Carhart) to fire a few shots at a fleeing criminal, although he misses and the criminal commits suicide by driving off a cliff. Also carried by various police officers.
A Glock 26 pistol is the duty weapon of the B.A.U.'s 'Communications Liaison' SSA Jennifer 'J.J.' Jareau (A.J. Cook). The Glock 26 is also the backup weapon carried by both Aaron Hotchner (Thomas Gibson) and Derek Morgan (Shemar Moore), both carried in ankle holsters.
SSA David Rossi (Joe Mantegna) carries a Springfield Armory TRP, a model of which is used by the FBI's elite HRT, throughout the series, this suggests he may have been HRT/SWAT trained to use this weapon. Rossi also has a background of serving in the U.S. Marine Corps, which also possibly helps explain his use of a 1911-type pistol.
The Beretta 92FS is a common firearm seen in the series, usually by Unsubs and police officers. Terrorist Ben Abner (Adoni Maropis) uses the Beretta upon exiting a hospital elevator in "Mayhem" (S4E01).
A female serial killer is seen pulling what appears to be a SIG-Sauer P232 on one of her victims in a Dallas parking garage in the episode "Pleasure Is My Business" (S4E16).
Dr. Spencer Reid (Matthew Gray Gubler) carries as his main weapon a 3" barrel Smith & Wesson Model 65 with wood-colored grips starting in the episode "The Angel Maker" (S4E02). He carries his sidearm in a very frontal appendix-carry (as he also did with his previous Glock 17), a manner in-which a militia leader once said "The way you wear that gun - you're just asking someone to take it off of ya." In addition, he carries the double-action revolver in a holster that does not cover the trigger guard, something that is not generally advisable. There are several good shots of it in Season 4, notably at the beginning of "The Instincts" (S4E06) when him and other agents check a basement (which actually happens to be a dream of Reid's).
A serial killer called 'Animal' uses what appears to be an N-frame Smith & Wesson Model 27 / 28 .357 Magnum revolver (Most likely a Model 28) to kill at least six people (four of whom were cops) in "Brothers in Arms" (S4E10).
Error creating thumbnail: File missingSmith & Wesson Model 28 with 4" barrel and Hogue Grips - .357 MagnumFile:CriminalMinds-SW28-1.jpgCloseup on the barrel of the unsub's S&W N-frame .357 in "Brothers in Arms" (S4E10). Note the revolvers fairly large size and distinctive barrel taper.
Smith & Wesson Model 36
Standard J-frame Smith & Wesson Model 36 revolvers are used by numerous unsubs (short for 'unknown-subjects') throughout the show. One Model 36 is notably seen wielded by a female unsub at the end of "The Angel Maker" (S4E02).
Identified as a .44 Magnum, a Smith & Wesson Model 629 V-Comp is used as the weapon of choice for
George Foyet aka 'The Boston Reaper' (C. Thomas Howell), an infamous serial killer and the nemesis of Agent Hotchner (Thomas Gibson). He uses it throughout "Omnivore" (S4E18) and also fires it at Hotch at the conclusion of Season 4's two-part finale.
Throughout the series, FBI SWAT and several local police tactical units carry M4A1 carbines, both standard models and variants with various accessories.
Another weapon used by the cult in "Minimal Loss" (S4E03) is the AKMSU carbine, notably the leader Benjamin Cyrus (Luke Perry). Like many AKMSUs in the film industry, these guns are outfitted with Krinkov parts kits to resemble AKS-74U carbines, but have a notably more curved 7.62x39mm magazine, as opposed to the AKS-74U's relatively straighter magazine.
Heckler & Koch MP5A3s are also used by various SWAT teams, notably by FBI SWAT in "Minimal Loss" during the rescue at the polygamist compound.
Heckler & Koch MP5A3 with Surefire dedicated forend weaponlight - 9x19mm.Error creating thumbnail: File missingIn "Minimal Loss" (S4E03), an FBI SWAT agent is armed with the MP5A3 while entering the polygamist compound.
Shotguns
Remington 870
In Season 4's two-part finale "To Hell" (Part 1) - "...And Back" (Part 2), former U.S. Army Sergeant William Hightower (Sharif Atkins), whose sister was abducted and later murdered by an unsub team, takes an unguarded Remington 870 fitted with a Surefire dedicated forend weaponlight and speedfeed stock, using it to kill one of the unsubs after hearing his callous justification for his actions, dropping the weapon and surrendering to the agents after firing the fatal shot.
A sawed off Remington 870 Field Gun shotgun with raised barrel ribbing is used by the 'Road Warrior' killer (Mitch Pileggi) in the episode "Normal" (S4E11). The shotgun has been fitted a custom brace on the pump that attaches to his windowsill and allows him to rack the slide and fire from inside his car at motorists while driving.
