Law Abiding Citizen
The following weapons can be seen in the film Law Abiding Citizen:
WARNING! SPOILERS AHEAD!
3rd Generation Glock 17 pistols are carried by Philadelphia Police Department officers, including Detectives Dunnigan (Colm Meaney) and Garza (Michael Irby). Clyde Shelton (Gerard Butler) also uses a specially modified Glock 17 to disable Clarence Darby, one of the criminals who murdered his family.
A Philadelphia PD SWAT officer is armed with a Beretta 92FS when going to apprehend Shelton.
Harrington & Richardson Revolver
When alerted to the police raid, Clarence Darby picks up a Harrington & Richardson .22 from underneath a couch cushion to use on the police.
The revolver fires nine shots but the film says it only fires six.
Heckler & Koch MP5A2
Members of the Philadelphia PD SWAT team that arrest Shelton are armed with MP5A2 submachine guns with Surefire dedicated forend weaponlights.
Other SWAT members as well as FBI HRT members are armed with M4A1 carbines fitted with tactical lights.
Browning M2HB Heavy Machine Gun
One of the contraptions that Shelton uses in his quest to exact vengeance on the justice system is a remotely operated weapons platform fitted with a Browning M2HB heavy machine gun, which is used to attack the attendees of a funeral. Side note: the sound effects during this scene were not even close to correct. The audio was from a weapon with a much higher rate of fire and a higher pitch. It was more like the M240 than the M2.
The other weapon used in the remotely operated weapons platform is a M136 AT4 rocket launcher.
Guards at the prison are seen with Remington 870 shotguns.
Cell Phone Gun
Another of Shelton's contraptions is a cell phone gun that fires a single bullet when a call is received.