Not quite. At least one of the stand-in guns used by Clint Eastwood in the first movie was probably a 6½-inch barrelled M57 in .41. But there were at lest three guns so used, a common practice in filming in which production cannot be delayed for want of a single unique prop.
Sreenwriter and later director John Milius, who was brought in to rewrite the original script for "Dead Right," the original working title of the film, after Frank Sinatra and several others turned down the lead role, and Clint Eastwood took the part after insisting that the setting of the film be changed from New York to San Francisco, has one of the guns used in the film by Eastwood. It was Milius who added the *most powerful handgun* lines and *go ahead, make my day* lines for his lead character. And his souvenier of that filming is indeed a genuine, 6½-inch barrelled, 4-screw M29.
It's been suggested that maybe some of the shooting scenes were done using a 6-inch barrelled S&W M25 in .45 Long Colt, allowing the use of Hollywood "4-in-1" blanks, long a staple of Hollywood's cowboy films. Either .41 or .44 Magnum blanks would have required custom loads, an additional budgetary item of which there would have been a record kept. There may havce been an M57 used for the shooting of some of the film's publicity stills, from where some of the rumored *Dirty Harry used a .41 stories* came from.
Now look at the holes in the end of the cylinder in the following pics: .41, or a .44/.45? I've owned three M58 Smiths and two M27s, and I don't think that the gun in the top pic is a .41.
