Mossberg 590

The Mossberg 590 shotgun was introduced in 1987 (the same year as the Mossberg Mariner). The Mossberg 590 shotguns differ from the 500 series primarily because of the design of the cap for the shell tube. The 500 series shotguns are designed for easy swapping of barrels. The 590 magazine tube is designed for ease of cleaning and maintenance. The 'nub' at the end of the 590's magazine tube was originally designed for holding the ring of the M7/M9 Bayonet when the bayonet is attached to the lug underneath the barrel. Other versions of the 590 maintain this style of end cap, even those without bayonet lugs.