Mossberg 590S 12 Gauge Pump 20 in. M-LOK Ghost Rings
Video review
Expert review
About this product
The Mossberg 590S is a 12-gauge pump-action shotgun engineered for multi-shell compatibility and duty-ready modularity, featuring a 20-inch barrel with a cylinder bore choke, ghost ring sights, and an M-LOK forend. This platform serves as a bridge between traditional tactical shotguns and modern accessory systems, built on Mossberg's proven dual-action bar mechanism that the USMC's M1014 contract validated. At $667.99, it occupies a price point below specialized defensive tools like the Benelli M4 but above basic field models like the Stevens 555 series, offering a specific value proposition for the prepared civilian.
What is the Mossberg 590S 12 Gauge Pump used for?
This shotgun is primarily engineered for defensive applications, including home defense, tactical training, and as a duty-ready vehicle platform. Its ability to cycle 1.75-inch mini-shells up to 3-inch magnums provides significant operational flexibility that a fixed-chamber gun like a Stevens 555 Sporting O/U lacks, allowing users to tailor recoil and capacity for different scenarios. The ghost ring sight system provides a coarse but fast sight picture optimized for engagements inside 25 yards, while the M-LOK forend accepts white lights, vertical grips, or IR laser aiming devices.
How does the Mossberg 590S 20 in. compare to the Mossberg 590A1?
The 590S is superior in shell compatibility and accessory mounting, while the 590A1 retains an edge in ultimate durability for institutional abuse. The primary functional difference is the 590S's ability to reliably feed and cycle 1.75-inch mini-shells directly from the factory magazine tube, giving it a 13+1 capacity advantage the standard 590A1 cannot match without aftermarket parts. However, the 590A1 features a heavier-gauge steel receiver, a thicker barrel wall, and a metal trigger guard/safety, making it the more robust choice for agencies that prioritize absolute longevity over round-count flexibility.
What does the Mossberg 590S weigh and what are its dimensions?
The shotgun weighs 7.25 pounds unloaded and measures 39.5 inches in overall length with its 20-inch barrel. This makes it approximately 1.3 pounds heavier and 2.5 inches longer than a comparable the Stevens 334 Rifle in .308 Winchester, a trade-off for its higher close-range terminal effect and manual-action reliability. The balance point sits just forward of the receiver, which aids in managing muzzle rise during rapid fire, and the 14.25-inch length of pull accommodates most shooters wearing body armor or winter clothing.
Who is the Mossberg 590S 12 Gauge NOT for?
This is not a suitable primary firearm for waterfowl hunting, competitive clay shooting, or any user seeking a lightweight, fast-handling field gun. The cylinder bore choke and ghost ring sight are severe handicaps for breaking distant crossing targets or patterning tight shot strings at 40+ yards, roles where a dedicated sporting shotgun like the Stevens 555 with interchangeable chokes and a ventilated rib excels. Furthermore, its 7.25-pound weight becomes a liability during long carries in the field compared to a 6.5-pound over/under.
What's in the box with the Mossberg 590S?
The factory package includes the shotgun, one Accu-Choke cylinder bore tube pre-installed, a chamber flag, a basic cable lock, and the owner's manual outlining warranty and compliance information. Notably absent are any spare choke tubes, a cleaning kit, or snap caps typically included with higher-priced sporting models. The manual is critical for understanding the specific loading procedures for mini-shells, which require a different technique than standard 2.75-inch shells to prevent stacking malfunctions.
Is the Mossberg 590S worth it at $667.99?
At this price point, it represents a strong value for a shooter whose primary use case is defensive readiness and who values the multi-shell capability as a core feature. You are paying approximately $200-$300 more than a basic Maverick 88 Security model primarily for the M-LOK forend, ghost ring sights, and the engineered mini-shell compatibility, which is a justifiable premium if those features align with your intended use. For a buyer whose needs are purely recreational clay shooting or hunting, that same budget is better spent on a dedicated sporting platform.
Specs at a glance
Pros & cons
What works
- Accepts 1.75", 2.75", and 3" shells – offers a 13+1 capacity with mini-shells.
- Features a true M-LOK compatible forend – accepts modern light/laser mounts without a clamshell.
- Uses the proven dual-action bar pump mechanism – identical to the military-spec 590A1 for reliability.
- Weighs 7.25 lbs – balances weight for recoil management without being overly heavy for storage.
Trade-offs
- Ghost ring sights are not adjustable for windage – requires drifting the rear assembly, a 20-minute gunsmith task.
- The fixed pistol-grip stock has aggressive texturing – can be uncomfortable during extended dry-fire sessions without gloves.
- Lacks a factory-installed sling mounting point on the stock – requires an aftermarket stud or M-LOK adapter.
Key attributes
| upc | 015813516020 |
| manufacturer | Mossberg |
| manufacturer part number | 51602 |
| action | Pump Action |
| atf type | Shotgun |
| barrel length | 20" |
| caliber/gauge | 12 Gauge |
| capacity | 13 + 1 |
| chokes included | Cylinder Bore |
| color | Blue |
| length | 42.75 |
| magazine included | Tubular Magazine |
| model | 590S |
| package height | 7.75 |
| package width | 2.25 |
| product type | Shotgun |
| safety | Tang |
| shipping weight | 9.0 |
| sights | Ghost Ring |
| sights type | Adjustable Sights |
Frequently asked questions
- Is the Mossberg 590S compatible with aftermarket stocks and pistol grips?
- Yes, it uses Mossberg's standard 500/590 series receiver threading and will accept most aftermarket stocks designed for those models. The fixed pistol-grip stock can be replaced using a standard 1-⅛ inch socket wrench; the conversion process typically takes 15-20 minutes. Ensure any replacement stock maintains a minimum 13.5-inch length of pull to remain compliant with standard ATF measurement procedures for overall firearm length.
- Does the 20-inch barrel accept a choke tube system?
- Yes, it uses Mossberg's standard Accu-Choke thread pattern (not Benelli/Beretta Mobilchoke). The factory-installed cylinder bore tube can be swapped for any Accu-Choke compatible tube, including improved cylinder, modified, or full constrictions from brands like Carlson's or Tru-Choke. The barrel is threaded to accept tubes up to 3 inches in length, which is the standard for most aftermarket options.
- How long does standard shipping take to an FFL?
- Ironclad Armory processes in-stock firearms for shipment within 2 business days of cleared payment and FFL verification. Transit time via our contracted carrier (typically UPS Freight) is 3-5 business days to the continental US. You must contact your chosen FFL dealer in advance to confirm they will accept the shipment and provide their license to us—this step often adds 1-2 days to the overall timeline.
- Can I return the shotgun if it doesn't fit me?
- No, federal law (18 U.S.C. § 922) prohibits the return of a transferred firearm by a non-licensee to a dealer for a refund, except in the case of a legitimate warranty defect verified by the manufacturer. Fit and feel are not considered defects. We strongly recommend handling this or a similar model at a local range or retailer before purchasing. All sales are final upon transfer at your FFL.
- Does the M-LOK forend work with Picatinny rail sections?
- Yes, but you will need to purchase separate M-LOK to Picatinny rail adapter sections. The forend has M-LOK slots at the 3, 6, and 9 o'clock positions, each accepting standard hardware. A typical setup for a white light requires one 3-slot M-LOK rail section (available from Magpul or UTG for ~$15-$25) and a compatible light mount.
- Is the receiver drilled and tapped for a optic mount?
- Yes, the receiver is pre-drilled and tapped with a 6-48 thread pattern on the top, compatible with Mossberg's standard #8 scope base screws. This allows for the direct mounting of a Picatinny rail (sold separately) to host a red dot or low-power optic. The process requires a torque screwdriver set to 15-18 inch-pounds to avoid stripping the aluminum receiver threads.