the revolver comes from the firing of the cartridge, but is supplied by the user either through cocking the hammer or, in a double-action design, by just squeezing the trigger. Another significant advantage of revolvers is superior ergonomics, particularly for users with small hands. A revolver's grip does not hold a magazine, and it can be designed or customized much more than the grip of a typical semi-automatic. Partially because of these reasons, revolvers still hold significant market share as concealed carry and home-defense weapons. A revolver can be kept loaded and ready to fire without fatiguing any springs and is not very dependent on lubrication for proper firing. Additionally, in the case of double-action-only revolvers there is no risk of accidental discharge from dropping alone, as the hammer is cocked by the trigger pull. However, the revolver's clockwork-like internal parts are relatively delicate and can become misaligned after a severe impact, and its revolving cylinder can become jammed by excessive dirt or debris. Over the long period of development of the revolver, many calibers have been used. Some of these have proved more durable during periods of standardization and some have entered general public awareness. Among these are the .22 rimfire, a caliber popular for target shooting and teaching novice shooters; .38 Special and .357 Magnum, known for police use; the .44 Magnum, famous from Clint Eastwood's Dirty Harry films; and the .45 Colt, used in the Colt revolver of the Wild West. Introduced in 2003, the Smith & Wesson Model 500 is one of the most powerful revolvers, utilizing the .500 S&W Magnum cartridge. Because the rounds in a revolver are headspaced on the rim, some revolvers are capable of chambering more than one type of ammunition. The .44 Magnum round will also chamber the .44 Special and .44 Russian, likewise the .357 Magnum will safely chamber .38 Special, .38 Long Colt, and .38 Short Colt. In 1996, a revolver known as the Medusa M47 was made that could chamber 25 different cartridges with bullet diameters between .355" and .357". Revolver technology lives on in other weapons used by the military. Some autocannons and grenade launchers use mechanisms similar to revolvers, and some riot shotguns use spring-loaded cylinders holding up to 12 rounds. In addition to serving as backup guns, revolvers still fill the specialized niche role as a shield gun; law enforcement personnel using a "bulletproof" gun