Mossberg 590 was developed by O.F.Mossberg & sons company (USA) in the mid-1970s as a "mil-spec" (adopted for US Military) modification of the model 500 shotgun. "Militarization" include strenghtening of the receiver and other parts, installation of the vented heatshield around the barrel, bayonet lug and extended magazine.technically, m590 is the same (as m500) manually operated, pump-action smoothbore shotgun.Mossberg 590 is ectremely rugged and reliable gun. It is adopted by US Marine Corps and by many Police depts and Law enforcement agencies across the USA.