After been has been chased through the stairwell by the entities, he meets up with Ester, Isaac, and Captain Miller. After a discussion, he loads a magazine into a pistol and hands it to Isaac who then chambers a round. The next scene is a long shot of Isaac again chambering a round in his pistol. If he had, in fact, inadvertently chambered a round twice, there should have been a distinct sound of a full cartridge hitting the floor.