Corrected entry: During the fight in Dana's bathroom the Accountant does a tactical reload of his handgun after firing it. A tactical reload is a tactic to exchange a partial loaded magazine with a full magazine. The magazine that should have been the partial loaded from the weapon is empty in the accountant's hand. A trained person would have known the magazine in the weapon was empty and wouldn't have done a tactical reload. Plus, the slide on the weapon would have locked back indicating the magazine in the weapon was empty, not requiring a tactical reload.
The Accountant (2016)
1 corrected entry
Directed by: Gavin O'Connor
Starring: Ben Affleck, J.K. Simmons, Anna Kendrick, Jeffrey Tambor, Jon Bernthal
Continuity mistake: Whilst sitting having lunch, when the girl sits beside Ben Affleck, he removes the cup from his thermos, and sets it down to his right. A following shot shows the cup now on his left. (00:36:00)
Neurologist: Your son is different.
Young Chris' Father: Sooner or later, different scares people.
Correction: A tactical reload is to keep the magazine; either because it has some ammo, or in this case to not leave forensic evidence behind. The slide only locks back when it tries to chamber a round from an empty magazine; when it chambers the last round (he knows, because he counted), it closes as normal.