the firing mechanism and barrel one at a time. In contrast, other repeating firearms, such as bolt-action, lever-action, pump-action, and semi-automatic, have a single firing chamber and a mechanism to load and extract cartridges into it. A single-action revolver requires the hammer to be pulled back by hand before each shot, which also revolves the cylinder. This leaves the trigger with just one "single action" left to perform—releasing the hammer to fire the shot—so the force and distance required to pull the trigger can be minimal. In contrast, with a self-cocking revolver, one long squeeze of the trigger pulls back the hammer and revolves the cylinder, then finally fires the shot. They can generally be fired faster than a single-action, but with reduced accuracy in the hands of most shooters. Most modern revolvers are "traditional double-action", which means they may operate either in single-action or self-cocking mode. The accepted meaning of "double-action" has, confusingly, come to be the same as "self-cocking", so modern revolvers that cannot be pre-cocked are called "double-action-only". These are intended for concealed carry, because the hammer of a traditional design is prone to snagging on clothes when drawn. Most revolvers do not come with accessory rails, which are used for mounting lights and lasers, except for the Smith & Wesson M&P R8 (.357 Magnum), Smith & Wesson Model 325 Thunder Ranch (.45 ACP), and all versions of the Chiappa Rhino (.357 Magnum, 9×19mm, .40 S&W, or 9×21mm) except for the 2" and 3" models, respectively. However, certain revolvers, such as the Taurus Judge and Charter Arms revolvers, can be fitted with accessory rails. Most commonly, such revolvers have 5 or 6 chambers, hence the common names of "six-gun" or "six-shooter". However, some revolvers have 7, 8, 9, or 10 chambers, often depending on the caliber, and at least one revolver has 12 chambers (the US Fire Arms Model 12/22). Each chamber has to be reloaded manually, which makes reloading a revolver a much slower procedure than reloading a semi-automatic pistol. Compared to autoloading handguns, a revolver is often much simpler to operate and may have greater reliability. For example, should a semiautomatic pistol fail to fire, clearing the chamber requires manually cycling the action to remove the errant round, as cycling the action normally depends on the energy of a cartridge firing. With a revolver, this is not necessary as none of the energy for cycling