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Ray King (J.K. Simmons) is seen carrying what appears to be SIG-Sauer P229 in flashbacks to the Gambino massacre.
Glock 17
Brax (Jon Bernthal) along with some of his operatives are seen with the Glock 17. Christian "Chris" Wolff (Ben Affleck) also uses one at one point.
Heckler & Koch HK45T
What appears to be a Heckler & Koch HK45T fitted with a suppressor is seen in the hands of Brax (Jon Bernthal). The pistol is also used by one of his operatives. The Tru-Dot sights visible in the production still denote that this is a factory HK45T model.
Para-Ordnance Black Ops 1911 14.45
During the course of the film Wolff uses a Para-Ordnance Black Ops 1911 fitted with a threaded barrel, magazine well, a Surefire X300 weaponlight, and a SilencerCo Osprey suppressor. This is the 14.45 variant with a 14rd doublestack magazine.
Rifles
Daniel Defense MK18
Wolff fires what appears to be a Daniel Defense DDM4 MK18 fitted with a foregrip, light, Magpul MOE stock, suppressor and Leupold HAMR/Delta point optic sight during the final shootout. The rifle can be seen earlier in the back of Wolff's Airstream trailer.
Remington 700PSS
Some operatives are seen armed with what appears to be a Remington 700PSS while guarding a home.
Barrett M82A1M
Wolff is also seen firing a Barrett M82A1M, first to snipe cantelope from a mile away, and later in two separate fights.
Machine Guns
GE M134 Minigun
A GE M134 Minigun is discovered by FBI agents in Christian's house, mounted to cover the front yard.
Other
Weapons Cache
Wolff keeps a hidden cache of weapons inside a mobile trailer.
Special
Actor Ben Affleck underwent firearms training prior to taking on the role in the film.