 The handgun used by Harry Callahan, the .44 automag, was extremely  difficult to acquire. The studio eventually went to the guns  designer who, although retired, had enough parts in his basement to  build two guns for the production. They were serial numbered "Clint  1" and "Clint 2". One was modified to function with blanks for use  in the film, the other was left in its original configuration so  that Eastwood could fire it at a pistol range to familiarize himself  with its function.