The double-action trigger is based on the single-action trigger. The difference is that with the double-action trigger, which is also called a cocking trigger, when pulling the trigger, the hammer is first cocked and then, as the pulling motion continues, the shot is fired. With the single-action trigger, it is not possible to shoot solely by pulling the trigger; the hammer must first be cocked in a separate motion. In revolvers, cocking the hammer automatically causes the cylinder to rotate.