Factual errors: In the first murder, Eugene fires two rounds into the victim from a revolver, then walks away without ejecting the engraved shell casings later found at the scene.
Continuity: Megan fires more rounds than her revolver can hold without reloading.
Factual errors: When the killer is in the bathroom near the end of the film, he can clearly be seen to reload his pistol with spent ammunition. Spent cases have an indentation in the primer (the round bit in the middle of the back of the case) which are clearly visible in the rounds used in the scene.
Factual errors: In the final shootout between Megan and Eugene, he has an unlimited number of bullets.
Revealing mistakes: When Megan and Eugene are in the helicopter flying over the city, the red rotating beacon light is flashing in the passenger compartment where they are sitting. The red rotating beacons are located on the top and bottom of the fuselage of all aircraft and cannot be seen from the passenger compartment.
Revealing mistakes: When Eugene is in the bathroom reloading his revolver, all the shells he puts in the cylinder have the primers dimpled showing they have already been fired.
Factual errors: The movie hinges on shell-casings ejected from a pistol used to commit murder. But the pistol used is a revolver, which retains its empty casings. These are ejected only by automatics.