[686P]

An award winning cinematographer told me there is a real problem with filming firing guns, whether blanks are used or not. The problem lies in the timing of the camera's gate and viewfinder. A lengthy boring explanation follows.

Lengthy Explanation:
Film cameras alternately expose the film and then the view finder.

When the viewfinder is displaying the image the film is not being exposed.
When the viewfinder is not displaying the image the film is being exposed.

That means that when the cinematographer sees the flash, the film didn't.
That means that when the cinematographer doesn't see the flash, the film did.

Subsequently it cannot be assured that the muzzle flash made it onto the film without lengthy and tedious retakes of the shot. It's far easier to impose an after-affect of both sound and flash to sync the flash and get a blast that doesn't saturate the recording equipment.

If you watch black and white film, the flash is not always recorded even though the gun recoils. I've seen that occur in Combat (TV Series) many times.

True for colour or monochrome.