From what I have read, many of his magazines he ejected still had unfired rounds in them.
That means that if he ejected a magazine and someone tried to attack him, he still could shoot them because there was still a live round in the chamber.
My understandingis that one of the video games he played taught him to drop magazines early...and some still had fifteem rounds. But that sort of detail makes a lib’s eyes glaze over. So to simplify it, whenever magazine capacity comes up....Lanza had to do at least five swaps....and it didn’t slow him down one bit.