Staff Writer (Updated: 10/13/2016):
Militarized forms feature 18.5- or 20-inch barrels for a more compact offering consistent with close-quarters combat and door-breaching sorties. These weapons are available in 6-. 8- and 9-shell magazine forms. Law enforcement versions are under the 590A1 designation and appear with heavier-duty details including safeties, trigger rings and barrels - the latter available in 14-, 18.5- and 20-inch lengths. Despite their law enforcement classification, the 590A1 is still utilized by elements of the US Army. The Mossberg 590 is also a shotgun of choice for the US Marines.
The action of the Mossberg 590 remains the proven pump-action slide which directs any spend shell casings from the chamber and introduces an available fresh shell from the tubular magazine. Loading of the magazine is through a gate under the forward portion of the receiver. Spent shell casings are directed from the large ejection port along the right side of the receiver. The action is regarded as smooth and reliable, consistent with competing brands elsewhere. Ammunition types include slug, shot and non-lethal riot rounds.