Mossberg 590A1 12 Gauge
Model: 51663
Mossberg 590A1 12 Gauge
Model: 51663
Full Specifications
About This Firearm
The Mossberg 590A1 is the mil-spec build of the 590 line, certified to MIL-SPEC 3443G — the U.S. military's procurement standard for pump shotguns. That spec requires a heavy-walled barrel, a metal trigger guard, a metal safety button (not the polymer button on civilian Mossbergs), and proof-firing beyond commercial standards. The 9-shot configuration runs a 20-inch barrel and holds 8+1 with 2-3/4 inch shells at 116 oz (7.25 lbs) and 41.75 inches overall.
The parkerized finish on the barrel, receiver, and hardware handles humidity and field grime better than blued steel or anodized aluminum. Ghost ring sights come standard — front post and adjustable rear — which give a usable sight picture for slug work to roughly 75-100 yards with no aftermarket cost. The bayonet lug is there because MIL-SPEC requires it; civilian buyers rarely use it and it doesn't snag on anything.
The 590 series has been in U.S. military service since 1987, and the 590A1 has been the standard procurement variant since shortly after. That history is practical, not branding: the design has been vetted through four decades of military use, and the U.S. Army has placed repeat orders into the 2020s. Civilian buyers pay a premium over the base 590, but the value of that premium is concentrated in the heavy-walled barrel, the metal hardware, and the ghost rings — most owners who buy a 590A1 use all three.
Best For
Strengths & Limitations
- 8+1 capacity (with 2-3/4 inch shells) is the highest of any standard-configuration pump in this batch — four more rounds than the Remington 870 Express's 4+1 without any extension tube.
- Ghost ring sights ship standard. The adjustable rear ring and front post make precise slug shots possible out of the box — something the base 590 and the 870 Express can't do without aftermarket parts.
- MIL-SPEC 3443G certification means the metal trigger guard, metal safety, and heavy-walled barrel have been proof-tested to military requirements. Owners report the metal safety button is more positive than the polymer button on civilian 500/590 models.
- At 116 oz (7.25 lbs) unloaded and 41.75 inches long, it's the heaviest and longest pump in this batch. Loaded with 9 shells the weight climbs fast — a real consideration for smaller-statured shooters or anyone running it at high guard for extended periods.
- Buyers who don't plan to use slugs are paying for ghost rings they won't need. The base 590 covers buckshot duty for less.
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Frequently Asked Questions
What does MIL-SPEC 3443G actually require?
MIL-SPEC 3443G is the U.S. military's procurement standard for pump-action shotguns. It mandates a heavy-walled barrel (thicker than the standard 590 barrel), a metal trigger guard, a metal safety button instead of polymer, a bayonet lug, and proof-firing with high-pressure test loads above commercial standards. The spec doesn't require a steel receiver — the 590A1 still uses an aluminum alloy receiver like the base 590. What you're paying for is the heavy barrel, the metal hardware, and the additional proof testing.
Does the 590A1 accept aftermarket pistol grip or folding stocks?
Yes. The 590A1 shares the same stock mounting interface as the rest of the 500/590 family, so Magpul SGA, Hogue OverMolded, and Mesa Tactical Urbino stocks all drop on without modification. Most owners stick with the factory fixed synthetic stock — the 13.87-inch length of pull fits most adults, and pistol grip-only stocks make cycling under load awkward for users without dedicated training.
Will the 590A1 cycle 2-3/4 inch shells reliably, or does it prefer 3 inch?
The 3-inch chamber accepts both, and the twin action bars plus anti-jam elevator handle mixed shell lengths without issue. Standard 2-3/4 inch buckshot, slugs, and birdshot all run normally. Capacity figures assume 2-3/4 inch — load 3-inch shells and tube capacity drops by one round. Mini-shells (1-3/4 inch) won't cycle reliably without an Opsol Mini-Clip adapter, same as on the base 590.
