In which movie did Dirty Harry use an automatic gun?

Dirty Harry, played by Clint Eastwood, did not use an automatic gun in any of the "Dirty Harry" movies.

He is famous for using a .44 Magnum Smith & Wesson Model 29 revolver.

While revolvers and automatic pistols are both handguns, the key difference is that revolvers have a revolving cylinder that holds multiple rounds, while automatic pistols have a magazine that feeds rounds into the chamber.