Trivia: Dirty Harry's .44 Magnum was not the most powerful handgun in the world at the time. In fact, among firearms enthusiasts (such as screenwriter John Milius, an NRA Board Member), there were a few relatively-well-known examples of pistols that were more powerful. Perhaps best-known was that R.B. Rhodda & Co. of Calcutta had sold a number of side-by-side pistols in .303 British during the 1890's through the 1920's. The .303 is a relatively potent rifle caliber that is significantly more powerful than the .44 Magnum. With that said, I can certainly understand why an SFPD officer wouldn't be lugging around an unwieldy, side-by-side, two-shot pistol.
Trivia: Dirty Harry is reputed to be the film that significantly launched Clint Eastwood's film career and was released in 1971. Also released in 1971 was Play Misty For Me, which was Clint's directing debut. In this film, when Clint walks into the diner just before the bank robbery, the cinema on the right hand side of the shot is advertising Clint's other movie Play Misty For Me.
Trivia: After Harry has finally killed Scorpio, he takes out his police badge and tosses it into the nearby water. Clint Eastwood was initially very uneasy about doing this because he feared it would mean to the audience that Harry was quitting police work for good. Director Don Siegel argued that Callahan was simply irritated with the policing system that made it difficult to dispatch of the killer in the first place, but decided to co-operate with Eastwood and tell him that he could simply draw back his arm before thinking twice and putting it back in his pocket. Eventually Eastwood changed his mind and threw the badge into the water.
Trivia: In real-life, Andy Robinson (Scorpio) is a pacifist who dislikes guns. Every time he fired a gun during the early stages of principal photography, he would flinch violently, so director Don Siegel was forced to close down production for a time and send Robinson to a school where he would learn to fire a gun convincingly. In spite of this, he still blinks when he shoots.
Trivia: When Harry chases down Scorpio, who has kidnapped a busload of school children, the character has to leap from a trestle bridge on to the top of moving bus. If you watch the scene carefully, you will notice that it is not a stunt man making the jump - Clint Eastwood (Harry) performed it himself.