Question for firearm experts
This question applies to more movies than just The Untouchables, but this just happens to be the last instance I saw of the thing I'm curious about. When Nitti is trying to crawl down the rope and Ness is about to pull the trigger and shoot him, the camera zooms in on his gun. You can see that the trigger is already pulled before he changes his mind and flicks the hammer back in.
Wouldn't the gun already fire when you have the trigger pulled back like that? Is this some kind of safety precaution they take when filming with firearms? This isn't the first time I've seen a pulled trigger like this in a movie so I was wondering. Haven't fired a gun myself so maybe it's just something I'm missing.