In the original movie, Dirty Harry, they used a S&W Model 57 .41 Magnum
as a prop for the .44 Magnum.
Wiki....
"Dirty" Harry Callahan also helped popularize the Smith & Wesson Model 29 .44 Magnum revolver. The film initiated a modest increase in sales of the powerful handgun, which continues to be popular some thirty-five years after the film's release. Throughout the film Eastwood's Model 29 is lionized as an all-powerful instrument capable of sending assailants flying wildly through the air, while in reality the round is far less dramatic than depicted. The .44 Magnum round is not considered to be a practical caliber for urban police use due to excessive recoil (making target re-acquisition difficult) and over-penetration issues, which greatly increases the likelihood the bullet going through targets and injuring bystanders.
The gun used by Clint Eastwood in the filming of the movie was reportedly not a .44 Magnum. According to a story related by a member of the studio's prop department, Smith & Wesson did not have a Model 29 in stock at the time one was requested for filming. Instead, they used a Smith & Wesson Model 57 in .41 Remington Magnum. The Model 29 and Model 57 are identical except for minute differences in bore size, chamber dimensions, and exterior markings, none of which are visible in the film.
Another version of the Dirty Harry gun story: In the scene where we see Inspector Callahan drawing his oversized revolver for the first time, the gun used was a Smith & Wesson Model 29 in .44 Magnum with an 8 3/8" barrel, but subsequent shooting (both with the cameras and the gun) was conducted using a Smith and Wesson Model 25 in .45 Long Colt with a 6" barrel. The choice of .45LC over .44 Magnum was to use the standard "Four-In-One" blank cartridges, which were widely used in filming cowboy movies, and thus readily available (unlike blanks for a .44 Magnum, which the prop department would have had to fabricate from scratch.) As in the story above, the Model 25 and Model 29 are so similar that it would be impossible to distinguish them at a glance. However, the film's co-writer, John Milius, who owns the one of the original guns from Dirty Harry and its sequel, Magnum Force, has written in gun magazines that a .44 Magnum was indeed used for filming and publicity shots.
