The sidearm of choice for Michael Westen (Jeffrey Donovan) continues to be the SIG-Sauer P228 at the beginning of Season 4.
SIG-Sauer P226 (Nickel)
A nickel SIG-Sauer P226 is the sidearm of choice for fellow burned spy Jesse Porter (Coby Bell). He holds the SIG on Fiona in "Blind Spot" (S4E11) and uses it throughout the Season 4 finale "Last Stand" (S4E18).
SIG-Sauer P226
In "Past & Future Tense" (S4E07), former spy Paul Anderson (Burt Reynolds) uses the SIG-Sauer as his sidearm of choice. In "Dead or Alive" (S4E16), corrupt detective Pete Jackman (Raphael Sbarge) also carries a SIG-Sauer P226 and pulls it on Michael.
SIG-Sauer P239
In "Eyes Open" (S4E13), Walt Renson (Ricky Wayne) pulls a SIG-Sauer P239 pistol with a two-tone finish when he finds Sam and Michael in his home.
Beretta 92FS
Sam Axe (Bruce Campbell) carries a Beretta 92FS as his personal sidearm throughout the series. The Beretta has also seen use by various other characters throughout the series' run, in both suppressed and unsuppressed forms.
Beretta 92FS Inox
The Beretta 92FS Inox is used by con artist Nick Madison (Clayton Rohner) during a hostage situation in "Breach of Faith" (S4E04). Michael later is seen with the handgun.
In "Hot Property" (S4E14), a Colt Compact M1991A1 is carried by Fiona that later ends up in the hands of the thief Natalie Rice (Callie Thorne), who attaches a suppressor to it.
Glock 17
Glock 17 is the handgun frequently seen used by officers of the Miami Metro-Dade Police Department.
Glock 26
Throughout Season 4, Fiona carries the Glock 26 as one of her sidearms.
The Heckler & Koch P30 is Michael's new sidearm beginning in "Center of the Storm" (S4E09). In this episode, Cole (Jon Seda) is seen pulling a Heckler & Koch P30 after disposing of Michael's P228. Cole uses the P30 throughout the episode to threaten Michael as well as combat Matt Reece's thugs. At the end of this episode he gives it to Michael. From this point on in the show, it becomes Michael's sidearm.
Heckler & Koch P2000
In "Past & Future Tense" (S4E07), Vitali (V.J. Foster) carries a Heckler & Koch P2000. Michael is later seen with the handgun.
Heckler & Koch VP70
In "Brotherly Love" (S4E15), Michael hands off a Heckler & Koch VP70 to Sam that he says Fiona modified to fire three-round bursts.
Jericho 941FB Compact
In "Fast Friends" (S4E02), Lee (Ron Yuan), the right hand man of Ming Khan, pulls a Jericho 941FB Compact when accused of working with Jesse Porter. In "Where There's Smoke" (S4E08), Jacob's brother Eddy carries a Jericho 941FB Compact as his sidearm and is seen pulling it on Michael.
Smith & Wesson SW99
In "Fast Friends" (S4E02), Ming Khan (Byron Mann) carries a Smith & Wesson SW99 with a nickel-plated slide as his sidearm.
Smith & Wesson Chief's Special CS40
In "Dead or Alive" (S4E16), Michael notices that a Homeland Security agent is carrying a Smith & Wesson Chief's Special CS40 with a suppressor attached.
Smith & Wesson 4506
In Season 4's premiere "Friends and Enemies" (S4E01), a Smith & Wesson 4506-1 .45ACP pistol appears to be the handgun carried by the biker named Hunter (Andy Mackenzie).
Smith & Wesson 5906
In "Hard Time" (S4E13), Cruz (Manuel Uriza) is seen picking up a Smith & Wesson 5906 from the floor after escaping from prison.
Smith & Wesson 945PC
In Season 4's premiere "Friends and Enemies" (S4E01), Big Ed (Andrew Bryniarski) is armed with what appears to be a Smith & Wesson 945 Performance Center.
In "Blind Spot" (S4E11), a hitman armed with a suppressed Walther P99 is sent to eliminate Emily (Jean Louise Kelly). In "Brotherly Love" (S4E15), Michael takes a Walther P99 off one of Hector Rivera's henchmen.
In "Made Man" (S4E03), mobster Tony Caro (Nestor Serrano) is seen pulling out a 4" Smith & Wesson Model 500 and placing on a table when as he threatens Michael.
Smith & Wesson Model 686
Fiona disarms a parking lot attendant of his 686 in "Guilty as Charged" (S4E12).
Colt Magnum Carry
Fiona Glenanne (Gabrielle Anwar) twists the cylinder of her Colt Magnum Carry next to Mike's ear at the beginning of "Hard Time" (S4E10).
In Season 4's premiere "Friends and Enemies" (S4E01), both Michael and Vaughn (Robert Wisdom) are seen carrying Heckler & Koch MP5A2's fitted with a scope on a mission to find an illegal gunrunner. The MP5A2 is also the main weapon carried by Vaughn's men in several later episodes.
Heckler & Koch UMP
The Heckler & Koch UMP is used by several of Vaughn's men in Season 4's "Guilty as Charged" (S4E12).
Ingram MAC-10
In Season 4's premiere "Friends and Enemies" (S4E01), Fiona is seen loading a few MAC-10's before going to see a client. Later in the episode, Michael also wields two MAC-10's to try and intimidate a biker gang.
Mini Uzi
In "Where There's Smoke" (S4E08), One of Jacob's thugs carries a Mini Uzi during the kidnapping attempt. Michael is later seen with the SMG.
Shotguns
Mossberg 500
What appears to be a Mossberg 500 is held by a prison guard during a riot in "Hard Time" (S4E10).
Mossberg 500 Cruiser
In "Center of the Storm" (S4E09), Michael takes a Mossberg 500 Cruiser off a witness and then uses it to detonate an explosive improvised out of an air conditioner.
Mossberg 500 Cruiser (Foregrip and saddle shell holder)
A Mossberg 500 Cruiser fitted with a foregrip and saddle shell holder is a frequently used shotgun in the series.
Mossberg 500 Persuader (Folding Stock and Door Breaching Brake)
A frequent shotgun seen used in the series is a Mossberg 500 Persuader fitted with a police folding stock, saddle shell holder, and door breaching brake. In "Brotherly Love" (S4E15), Michael in his persona as the car thief Johnny uses the shotgun during a raid on Buckwild's chop shop.
Remington 870
In "Brotherly Love" (S4E15), Nate Westen (Seth Peterson) uses the Remington 870 Express Magnum fitted with a saddle shell holder during a raid on Buckwild's residence.
Saiga 12K
In "Center of the Storm" (S4E09), a modified Saiga 12K automatic shotgun is said to have been used in an attempted hit on an FBI witness.
Serbu Super Shorty
In "Eyes Open" (S4E13), Fiona pulls out her Serbu Super Shorty shotgun when told that a bomber was headed towards her home. In "Brotherly Love" (S4E15), Nate Westen (Seth Peterson) uses the Serbu Super Shorty shotgun fitted with a saddle shell holder during a raid on Buckwild's chop shop.
Assault Rifles
Colt Model 933
In "Breach of Faith" (S4E04), Miamo Metro-Dade SWAT officers are armed with the Colt Model 933.
Heckler & Koch HK416
One of the frequent weapons used by Jesse Porter (Coby Bell) in Season 4 is the Heckler & Koch HK416. In "Fast Friends" (S4E02), Jesse storms a gangster's compound armed with the rifle. In "Guilty as Charged" (S4E12), Jesse uses the Heckler & Koch HK416 to shoot Michael.
M16A2
An M16A2 is briefly seen in the hands of a Miami Metro Police officer during the standoff in Season 4's "Breach of Faith" (S4E4).
Norinco Type-56
A Norinco Type 56 rifle is seen in Season 4's premiere "Friends and Enemies" (S4E01).
SCAR-L
The FN SCAR-L is carried by Matt Reece's thugs in "Center of the Storm" (S4E09). It's used when when Michael beats down the thug, causing the weapon to go flying in the air.
SIG SG 552
The SIG SG 552 assault rifle is a frequently used weapon in the series. The rifle is used by one of Matt Reece's thugs and Matt Reece himself in "Center of the Storm" (S4E09). In "Guilty as Charged" (S4E12), the SIG rifles are used by Fiona and Sam throughout the episode.
Sniper Rifles
Heckler & Koch SL8-1
The Heckler & Koch SL8-1 is used in several episodes. In "Made Man" (S4E03), Michael uses a suppressed SL8-1 to shoot out the security guard's tires. Later, Michael and Fiona use 2 suppressed SL8-1s to shoot Gio's engine block. An SL8-1 is also used by Sam while providing cover for Michael in "Dead or Alive" (S4E16). Sam takes aim at Larry with an SL-8 fitted with a laser sight and suppressor in "Out of the Fire" (S4E17).
Remington 700 AICS
A Remington 700 AICS is used by Sam as he provides cover in "Guilty as Charged".
Remington 700PSS
A Remington 700PSS is seen being used by one of Vaughn's men when Simon attempts to escape at the beginning of "Hard Time" (S4E10). Later in the episode, a prison guard takes aim with a different Remington 700 during a riot.
Heavy Weapons
Barrett M107
In "Fast Friends" (S4E02), Barrett M107 rifles are among the weapons supplied by Michael to Ming Khan.
M136 AT4
In Season 4's premiere "Friends and Enemies" (S4E01), an M136 AT4 is among the weapons seized by Vaughn (Robert Wisdom) when on a mission to find an illegal gunrunner.
Ramo RT-37
What appears to be the heavily-modified Ramo RT-37 riot control launcher used in the Transformers films is first seen among the weapons supplied by Michael to some gangsters in "Fast Friends" (S4E02). The launcher, fitted with a red dot sight (appears to be a Bushnell Holosight) and M4 type stock, is also used by Jesse Porter (Coby Bell) in "Neighborhood Watch" (S4E05).
Fictional Gatling Gun
A CGI-created eight-barreled Gatling Gun is seen firing from underneath an MQ-1 Predator UAV in order to assassinate a rogue arms dealer (Michael Ironside) in "Friends and Enemies" (S4E01).
Other
Advanced Taser X26
What appears to be an Advanced Taser X26 is used by a Metro-Dade SWAT officer in "Breach of Faith" (S4E04).
M18A1 Claymore Mine
In "Center of the Storm" (S4E09), Cole (Jon Seda) sets up a M18A1 Claymore as a booby trap that Michael stumbles upon.
Michael's Gun Cache from "Fast Friends"
In "Fast Friends" (S4E02), several weapons are supplied by Michael to Ming Khan.
Captured Gun Cache from "Friends and Enemies"
Vaughn's men uncover several weapons from an arms dealer in Season 4's premiere "Friends and Enemies" (S4E01).