To fire again, the hammer must be manually cocked again. This is called "single-action" because the trigger only performs a single action, of releasing the hammer. Because only a single action is performed and trigger pull is lightened, 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. Unfortunately with some revolvers, since the hammer rests on the primer or nipple, accidental discharge from impact is more likely if all 6 chambers are loaded. The Colt Paterson, Colt Walker, Colt Dragoon, and Colt Single Action Army of the American frontier era are all good examples of this system. Double-action In double-action (DA), the stroke of the trigger pull generates two actions: The hammer is pulled back to the cocked position which also indexes the cylinder to the next round. The hammer is released to strike the firing pin. Thus, DA means that a cocking action separate from the trigger pull is unnecessary; every trigger pull will result in a complete cycle. This allows uncocked carry, while also allowing draw-and-fire using only the trigger. A longer and harder trigger stroke is the trade-off. However, this drawback can also be viewed as a safety feature, as the gun is safer against accidental discharges from being dropped. Most double-action revolvers may be fired in two ways. The first way is single-action; that is, exactly the same as a single-action revolver; the hammer is cocked with the thumb, which indexes the cylinder, and when the trigger is pulled, the hammer is tripped. The second way is double-action, or from a hammer-down position. In this case, the trigger first cocks the hammer and revolves the cylinder, then trips the hammer at the rear of the trigger stroke, firing the round in the chamber. Certain revolvers, called double-action-only (DAO) or, more correctly but less commonly, self-cocking, lack the latch that enables the hammer to be locked to the rear, and thus can only be fired in the double-action mode. With no way to lock the hammer back, DAO designs tend to have bobbed or spurless hammers, and may even have the hammer completely covered by the revolver's frame (i.e., shrouded or hooded). These are generally intended for concealed carrying, where a hammer spur could snag when the revolver is drawn. The potential reduction in accuracy in aimed fire is offset by