In a single-action revolver, the hammer is manually cocked. This is usually done with the thumb. This action turns the cylinder to the next cartridge. It also locks the cylinder in place with the chamber aligned with the barrel. The trigger, when pulled, releases the hammer, which fires the round in the chamber. To fire again, the hammer must be manually cocked again. This is called "single-action" because the trigger only performs a single action—that of releasing the hammer. Because only a single action is performed and trigger pull is very light, firing a revolver in this way allows most shooters to achieve greater accuracy. Additionally, the need to cock the hammer manually acts as a safety. The gun will not fire unless the hammer is cocked back. The Colt Paterson Revolver, the Walker Colt, the Colt's Dragoon and the Colt Single Action Army pistol of the American Frontier era are all good examples of this system.