Continuity mistake: In the early scene when Harry walks across the street to confront the wounded robber on the street ("Did he fire six shots or only five?"), the shotgun used by the robber is lying several feet from the robber's hand, but when he reaches the robber, the camera shot shows the shotgun just a few inches from the robber's left hand. (00:13:00)
Continuity mistake: During the scene on the football pitch where Callahan is torturing Scorpio to force him to say where the kidnapped girl is, there are several shots as if from Callahan's viewpoint. As the camera switches between the two characters, the white painted lines on the pitch mysteriously move or even vanish underneath Scorpio. (01:06:50)
Factual error: When Harry is confronting the bank robber and the robber says he has to know if Harry had any shots left, Harry cocks the hammer which rotates the cylinder. If you watch closely when he pulls the trigger the cylinder rotates again. This can happen only when the trigger is pulled in double action mode (hammer down). (00:14:00)
Continuity mistake: When Scorpio leaves the hospital after treatment of his face injuries he has a band aid over his nose and a rectangular gash on the forehead. When he kidnaps the bus the tape is higher up his nose, and after he hits the little boy it is shorter. The gash on the forehead turns triangular at the end before they crash into the gravel pit area. (01:30:00)NancyFelix
Revealing mistake: Near the end the psycho killer pays a black man to beat him up so that he can then blame the injuries on Dirty Harry. Watch the killer's hairdo as he gets punched and beaten: a couple of rear-view scenes show an obviously fake wig, intended to look like the killer's own bad-hair-day style. (01:16:05)
Continuity mistake: When Scorpio shoots the girl in the pool a red towel is spread over the backrest of the right deckchair. When the police officers are dealing with the girl's body the towel is crumpled in the seat of the chair, but when Harry looks at the pool from the other building the towel is again spread out as before. (00:02:00 - 00:04:30)NancyFelix
Continuity mistake: When the jumper jumps over to the cabin in which Harry was lifted up, Harry knocks him out, securing the man by holding his arm over the top railing. When they arrive on the ground he is holding the man's arm over the lower railing, which raises the question how and especially why he moved the unconscious man down while he was hanging outside the cabin. (00:31:10)NancyFelix
Plot hole: When Harry is on the roof of the first shooting, he finds the spent shell casing. Later in the office he says that they think it is a 30-06. He has the shell casing. He *knows* if it is a 30-06 or not.