The following weapons were used in the film Chicago:
Smith & Wesson Model 12
At the beginning of the film, Roxie Hart (Renée Zellweger) uses her husband's Smith & Wesson Model 12 to kill her lover Fred Casely (Dominic West). The same weapon is later seen as evidence at Roxie's trial being handled by her lawyer Billy Flynn (Richard Gere).
Colt Detective Special
Kitty Baxter (Lucy Liu) takes a nickel plated, third generation Colt Detective Special out of her drawer to murder her husband and his two mistresses. The weapon appears to have ivory grips though it is hard to tell for certain. It should be noted that the weapon is anachronistic, as the Colt DS didn't start production until 1927, and the film takes place in 1924. The third-generation models didn't come out until the mid-70s.
Colt Police Positive
At the end of Roxie's trial, an unknown woman is seen on the street holding a nickel planted Colt Police Positive after having just shot a man.
In the opening scene, Velma Kelly (Catherine Zeta-Jones) is seen hiding an unknown nickel plated revolver she recently killed her husband and sister with.
At the end of the film, Roxie and Velma are seen performing a vaudeville show with white Thompson Submachine Gun stage props.