If you are absolutely certain that it is not cocked, nothing would happen if you are referring to a percussion Colt 1860 Army model. It would not fire. It is a single action mechanism only, which means it has to be cocked to fire. If the revolver was double, single action both (which an 1860 Army is not) and the hammer was not cocked, it would still fire in double action when you pulled the trigger. But regardless of what type of weapon it is, it is not a