The following weapons were used in the film American Psycho:
Patrick Bateman (Christian Bale) carries a Glock 19 when he goes on his shooting rampage through New York City, inexplicably blowing up a police car when he fires at it. In the novel, Bateman uses a ".357 Magnum" kept in a holster, which he later attaches a suppressor to. Suppressors generally don't work on revolvers, as Bateman soon finds out, when he kills a homeless man with it and, not realizing the ineffectiveness of a suppressed revolver, the gunshot nearly deafens him.
Heckler & Koch P7M8
One of the "Charlie's Angels" dancers at the club during the film's opening holds a Heckler & Koch P7M8 pistol.
Ruger Mark II
One of the "Charlie's Angels" dancers at the club during the film's opening is holding what appears to be a Ruger Mark II pistol with a long, tapered barrel.
One of the "Charlie's Angels" dancers at the club during the film's opening holds a Walther PPK pistol.
Smith & Wesson Model 10 HB
A New York City policeman fires his heavy-barreled Smith & Wesson Model 10 at Bateman during the rampage.
Patrick Bateman keeps an Ithaca 37 with a pistol grip in his kitchen weapons cabinet, which is seen when he retrieves duct tape from it when his secretary, Jean, (Chloë Sevigny) is over at his apartment. It is nestled in the corner next to the chainsaw and has a pistol grip.