sentences:  One can cock the hammer (the action of which moves levers to rotate the cylinder and align a fresh cartridge with the rear of the barrel), then pull the trigger for each shot ("single-action mode") or one may simply pull the trigger, through a longer, heavier stroke.This causes levers and springs to both rotate the cylinder and draw the hammer to the rear, then release it, firing the cartridge.Firing a double-action revolver in single-action mode tends to be more accurate, because the trigger pull is much shorter and lighter; usually three or four pounds-force (18−22 newtons) of pull is sufficient, instead of the twelve to twenty pounds (50−90 N) required for double-action mode, so the firearm's aim and mobility is less likely to be disturbed by the force of pulling the trigger.