The study of the sequence and trajectory of bullets that struck Ms Steenkamp through a closed toilet door is at the centre of testimony over her body position and how rapidly Pistorius fired the fatal shots.
Police say Ms Steenkamp, a 29-year-old model and television personality, was cowering with her hands over her head when she was hit in the head.
But Wollie Wolmarans, a private ballistics expert, testified for the defence that he did not believe her left hand was over her head.
The painstaking debate over detail reflects the defence's efforts to show Ms Steenkamp was not arguing with Pistorius when she was shot in the early hours of February 14 last year, as the prosecution contends.
Pistorius, 27, is charged with the premeditated murder for Ms Steenkamp. He says the killing was accidental because he mistook her for an intruder. The athlete held his hands over his ears in court when Mr Wolmarans talked about Ms Steenkamp's wounds.
Pistorius faces 25 years to life in prison if convicted of premeditated murder. His fate will be decided by a judge, as South Africa does not have trial by jury.