A nickel Colt MK IV Series 70 is the handgun carried by Bobby (Mark Wahlberg), which he hands off to Angel (Tyrese Gibson) from the trunk of his car during a scene of trying to get information about their mother's killers. Bobby later uses it to shoot at Damian's dogs and then at Damian as he escapes. Bobby also uses the pistol to execute one of his mother's killers after the car chase scene.
One of Victor Sweet's thugs produces a custom ported Desert Eagle Mark I and fires a shot into Jack's shoulder, wounding him. Bobby (Mark Wahlberg) then picks up this same gun off the ground after the gunfight and shoots another thug pointblank after getting information out of him. The same gun can be seen in The Big Hit (ironically, another movie that starred Mark Wahlberg).
One of the guns that Bobby (Mark Wahlberg) retrieves from the shooters' apartment is a Beretta 93R with the fore grip and flash hider removed. This appears to be the exact same weapon that Mark Wahlberg previously used in The Big Hit, and its appearance in the movie is likely a reference to Wahlberg's appearance in that film. (Both The Big Hit and Four Brothers acquired their weapons from the same armorer - John "Frenchie" Berger.)
One of the shooters employed by Victor Sweet (Awaovieyi Agie) fires a Beretta 92FS Inox at Bobby's car during the car chase scene. A Beretta Inox is also used by Angel during the home shootout.
Detective Fowler (Josh Charles) uses a Glock 17 as his issued sidearm and draws it when there's a knock at the door in one scene. Angel (Tyrese Gibson) obtains it from Fowler and holds him at gunpoint, Fowler then retrieves the pistol again and holds Angel hostage, then fires shots at the Detroit police before being shot.
Damian (Lyriq Bent) retrieves a Ruger P90 from his apartment when the Mercer brothers come banging on his door. He then fires a few shots at them when attempting to escape. Angel (Tyrese Gibson) then uses this pistol throughout the rest of the movie, specifically during the car chase scene.
One of the weapons that Bobby takes from the shooter's apartment is a SIG-Sauer P220 Sport which Angel later uses in the home shootout, and one of Victor Sweet's men can be see with one just before the meeting.
What appears to be a nickel Smith & Wesson Model 19 is seen amongst the various guns Bobby (Mark Wahlberg) ransacks from the shooters home, he aims it at Jerry when he arrives at the Mercer home suddenly unannounced while he and Jack sort through the ransacked guns.
Detective Fowler (Josh Charles) uses a Smith & Wesson Model 60 .38 Special revolver with a bobbed hammer to commit a murder. Fowler then wipes off his fingerprints and ditches the revolver.
When Bobby lifts the mattress to reveal the shooter's arsenal, a pair of small frame snub nose revolvers that resemble the Smith & Wesson Model 36 are seen.
A Remington 870 is used by the robbers at the beginning to kill the store owner and Evelyn Mercer (Fionnula Flanagan). Bobby (Mark Wahlberg) also uses a pistol gripped Remington 870 throughout much of the movie, and once used by Jack (Garrett Hedlund) as the shooters escape in their car. In a continuity error, Bobby's Mossberg changes to the 870 during the house shootout, seen below.
Bobby (Mark Wahlberg) finds a Mossberg 500 Cruiser (the pistol gripped version of the Mossberg 500) in the shooters' apartment. Bobby uses this shotgun specifically in the Mercer home shootout scene to kill multiple thugs. In a continuity error, the gun changes to the Remington 870 above during the shootout. This can be seen in the above screencap of Bobby blind firing the 870 during the shootout, when it was a Mossberg just moments earlier.
A couple of Victor Sweet's hoodlums use Heckler & Koch G36Cs in an attempted hit on the Mercer brothers in their mother's home, one of them fitted with a G36E-esque carry handle/sight assembly.
A SWAT team member uses a Heckler & Koch HK33A2 with scope and bi-pod to shoot and kill a crazed Detective Fowler (Josh Charles). It appears to be fitted with the 30 round magazine that was introduced with the HK93 civilian rifle.
At Lt. Green's (Terrence Howard) funeral, police officers in the honor guard can be seen firing M16 (SP1) rifles mocked up to resemble M16A2s - they are fitted with heavy A2-style barrels as well as A2-style handguards, and feature 20 round magazines.
Error creating thumbnail: File missingM16 aka SP1 (flat "slab side receiver") with A2 style handguards to resemble the M16A2 - 5.56x45mmError creating thumbnail: File missingAn honor guard uses the rifles to perform a rifle volley at a police funeral. Note the lack of forward assist or magazine fencing, indicating it is a SP1 reciever mocked up with A2 handguard and heavy barrel to resemble an M16A2.
Remington Model 700PSS
Just before the police go to Fowler's house, a SWAT officer can be seen with a Remington Model 700PSS slung over his shoulder.
