The Mossberg 590S Shockwave 18.5-inch 12 gauge is a pump-action firearm with a 3-inch chamber and a nine-shell tubular magazine (brand part no. 51600). The S in 590S marks Mossberg’s multi-shell design, which cycles 1.75-inch mini shells alongside standard 2-3/4-inch and 3-inch loads without an adapter. The 18.5-inch barrel and long magazine tube give this version far more capacity than the short-barrel Shockwave models. A bead sight, a cylinder bore choke and an ambidextrous top-tang safety keep the controls familiar for anyone who has run a 500 or 590. It suits home defense and range use where a high shell count matters more than the shortest possible length.

Key Specifications

• The gauge is 12 gauge, with the widest choice of defensive and practice loads.
• Chamber length is 3 inches, covering standard and magnum 12 gauge shells.
• The 590S design cycles 1.75-inch, 2-3/4-inch and 3-inch shells, so mini shells can be mixed with full-size loads.
• Barrel length is 18.5 inches, which supports the longer magazine tube on this version.
• Capacity is 9+1 from the tubular magazine, nine in the tube and one in the chamber.
• The action is pump action, manually cycled for reliability across shell lengths.
• The safety is an ambidextrous top-tang safety, reachable with either thumb.
• Sights are a fixed bead, quick to pick up at close range.
• The included choke is cylinder bore, a common choice for buckshot and slugs.
• The barrel finish is matte blued, a low-glare finish on a black gun.

Frequently Asked Questions

Can it shoot mini shells? Yes. The 590S design cycles 1.75-inch mini shells as well as 2-3/4-inch and 3-inch shells, with no adapter needed.

How many rounds does the 18.5-inch version hold? Capacity is 9+1: nine shells in the tubular magazine and one in the chamber.

What choke does it use? It comes with a cylinder bore choke, an open choke suited to buckshot and slugs.

Buy the Mossberg 590S Shockwave 12 Gauge, 18.5-Inch, Black, 9+1

Shooters who like the Shockwave’s handling but want more shells on board will find that in the 18.5-inch 590S. Order it through Mossberg‘s pump-action lineup from our Lubbock, Texas gun shop for fast, insured shipping to your FFL.