different barrels, as the barrel is held in place by attaching at the end of the magazine tube. The shortest barrel length available for the eight- and nine-shot models is , which fits flush with the long magazine tube. A ribbed modified choke field barrel was also manufactured for the 8-shot model 500. The shortest barrel for Title I six-shot models is , while military and law enforcement personnel (as well private persons in NFA states) can also get a barrel (the 590 Compact), which uses a special 5-shot magazine. Model 500 variants The Model 500 is available in many variants, for a wide variety of applications. The ease of changing barrels on the Model 500 means that a single shotgun may be equipped by the owner with a number of barrels, each for a different purpose. As sold, the Model 500 is generally classed into two broad categories: field models and special purpose models. Field models Field models are the basic sporting models. They are available with a variety of barrel lengths and finishes, and may be set up for waterfowl hunting, upland game hunting, turkey hunting, or shooting slugs. Most smoothbore models come with interchangeable choke tubes and vent rib barrels, while the slug models come with rifle sights or scope bases, and may have smooth cylinder bore or rifled barrels. Special purpose models Special purpose models are intended for self defense, police, or military use. The Model 590 and the eight-shot Model 500s are only sold as special purpose models. Special purpose models have short barrels, either for the six-shot models, or for the eight- and nine-shot models, but the barrels are fully interchangeable with all models of the same magazine tube length and in the 500 family. Most models come with special designations like SPX, Tactical, Mariner, etc. Special purpose models may be equipped with a variety of specialty parts which may include adjustable stock, "Speedfeed" stock that holds four additional rounds of ammunition, pistol grip, ghost ring and fiber optic sights, Picatinny rail, forearm band, heatshield, ported barrel, muzzle brake, and even a bayonet lug. All special purpose models come only in black trim with either blued, non-glare matte blue, or parkerized finishes and now come with drilled and tapped receivers for scope and optics mounting. "Special Purpose" models are not the same as "Law Enforcement" models; the latter have heavier duty barrels, safeties, trigger