Continuity mistake: In the scene where Maggie goes to the restaurant with Bob, he offers her the case where the weapon is. Bob says, 'It's loaded'. Close inspection shows the clip chamber is empty (not loaded), and a cartridge clip is positioned beside the weapon in its tailored slot in the custom case. Maggie closes the case and says, 'I don't understand.' After Bob explains what she is to do, then leaves, Maggie opens the case again and suddenly there's a clip in the weapon (loaded) and another one beside it. The weapon was not loaded when she looked the first time.
Factual error: When Nina was given the assignment in the restaurant in the guise of a dinner outing,she was handed a a box with a pistol in it. That pistol was an Olympic-grade target pistol used in international competition. That type of firearms does NOT hold 8 rounds,and she fired 8 rounds before re-loading.
Other mistake: In the scene where Nina assassinates a woman from the hotel room with a rifle, she kills her with three or four shots. The rifle she had was a bolt action and could not be fired that quickly.