Ove Kjikerud (Eivind Sander) own a Beretta 92 Steel I, which he keeps in his refrigerator. The gun is shown seamlessly transitioning from firing blanks to firing live rounds. Roger Brown (Aksel Hennie), Clas Greve (Nikolaj Coster-Waldau) and Diana Brown (Synnøve Macody Lund) also get their hands on the pistol during the course of the film.
While Googling Clas Greve, Roger comes across a few pictures of Clas from his Army days, including one where he's holding an M4A1 carbine with an underbarrel M203 Grenade Launcher.
Error creating thumbnail: File missingM4A1 carbine 5.56x45mm with M68 Aimpoint red dot scope, flip-up rear sight, and M203 grenade launcher 40mmError creating thumbnail: File missingThe image is most likely a photoshop, as the guy next to Clas, who is supposed to be Dutch, has an American 82nd Airborne patch, and everyone is wearing American ACUs. Clas also wears the American rank of Corporal.
Mini Uzi
Ove also own a fully automatic Mini Uzi, which Roger Brown later uses.