Both the Model 500 and Model 590 have polymer trigger guards and safeties, and standard barrels. The Model 590A1 has an aluminum trigger guard and safety, a heavier barrel, and a bayonet lug (although some versions of the 590 also have bayonet lugs), intended for military use under extreme conditions and rough handling; the metal trigger guard was added in response to the 3443G materials requirements, and the heavy barrel was added at the request of the Navy to prevent barrel deformation if the shotgun caught in the closing of heavy steel ship doors. Some 590A1s have a sling swivel on the back of the bayonet lug, some do not. The 590A1 usually has a swivel mount on the stock even when there is no corresponding mount on the forward end of the weapon. The 590A1 is generally sold through military and law enforcement channels, though in most jurisdictions the 18. 5-inch (47 cm) and 20-inch (51 cm) barreled models are available and may be legally purchased by any non-prohibited persons. 590A1s with 14" barrels are Title II firearms, and may be purchased only by non-prohibited persons in NFA-legal states, after completing BATF transfer forms.