On cap and ball, many people grease the chamber to seal it. You’ll only see black powder lube at the front of the cylinder, and not the bullet under it.
As you no doubt know, but for others, a black powder pistol almost guaranteed it was a single action requiring thumb cocking of the hammer before shooting.
Thus Alec had to cock the hammer, point the pistol at the female cinematographer and then pull the trigger...all deliberate actions. A noose would be period appropriate.