You usually don't see them being chambered; you just hear the sound of the weapon being cocked. That's entirely the fault of the folly editors who think that it sounds cool to hear guns being cocked all the time.

I mean like you see a cop drawing his gun and then racking the slide to chamber a gun. It would have been tactically sound to have already chambered a round.

drawing a handgun from a leather holster and hearing the pump action shotgun noise.....

Hmmm, I really haven't seen that very much. Not enough to be a "law" anyway. Again, though, I know it's common to hear the sound of rounds being chambered or hammers being cocked when cops draw their weapons. But I don't recall too many movies where I can see it happening on-screen.

"guns are full of ball bearings that rattle around when the gun is even slightly moved"

Drawing a gun from a holster always makes a loud WHOSH sound.

They always pull the hammer down to mean business and ride the hammer back down when they are being nice

The main antagonist has extra lives

The main bad guy is always last to fall, they never have them die and then just mop up the thugs, you mop up the thugs and then go into a final confrontation....

The Villain never knows the difference in weight between a loaded and an unloaded gun.

When the main characters tells a villain that the safety is on, the guy will always look at the gun on reflex just long enough for the main character to grab and disarm.

A revolver doesn't have a safety, but when you tell someone the safety is on, he'll look.

A Glock doesn't have any external hammer or safety, yet when pointed at someone off camera, it always makes a hammer or safety sound before the camera brings it into view.