I posted this twice on the corrections thread, and it was taken down both times without any comment. Perhaps its more appropriate for this thread?
From page 171. “Loaded Revolvers The chamber directly under a revolver's hammer is often left empty against an accidental discharge. If this practice is followed, lower the ammunition capacity by 1. To emphasize the danger of carrying a fully-loaded revolver, your gamemaster may require your character to make a successful Luck roll to avoid an accidental discharge if your character falls or is jostled roughly enough to potentially trigger the weapon. If the Luck roll succeeds, the revolver does not go off. If it fails, the revolver goes off, and your character and everyone around your character must make a Luck roll to avoid being hit by the stray bullet. Your gamemaster should determine who the friendly fire strikes. If the initial Luck roll is a fumble, the bullet strikes your character and does normal damage.”
This should only apply to early revolvers, and those from about the late 19th century onwards should be safe with all chambers loaded.