Mossberg 500A 12ga 24" Rifled Slug barrel

Mossberg 500A 12 Gauge Shotgun with 24" Rifled Slug Barrel

The Mossberg 500A refers to an early variant of the iconic Mossberg 500 pump-action shotgun series, introduced in the 1960s. The "A" designation often denotes the original field model with a standard 28" smoothbore barrel, but Mossberg shotguns are highly modular, allowing easy barrel swaps. The configuration you described—chambered in 12 gauge with a 24" rifled slug barrel—is a popular upgrade for deer hunting, big game, or improved accuracy with sabot slugs. This setup transforms the versatile 500 into a dedicated slug gun while retaining its compatibility with birdshot or buckshot via other barrels.

Key Specifications

Based on Mossberg's official product details for compatible 24" rifled slug barrels (e.g., models like 90120, 3905MT, or 90055), here's a breakdown:

Feature

Details

Gauge

12 Gauge (3" chamber)

Barrel Length

24 inches

Barrel Type

Fully rifled (for slugs), cylinder bore (no choke), 1:36 twist rate for stability

Sights

Adjustable rifle-style sights (front post and rear peep); some variants include fiber optic or integral scope bases

Finish

Matte blued or parkerized steel (resistant to corrosion)

Porting

Optional vented ports to reduce muzzle rise (e.g., on 3905MT model)

Weight (Barrel Only)

Approximately 3-3.5 lbs

Compatibility

Fits Mossberg 500, 500A, and Maverick 88 6-shot models (not compatible with pistol-grip variants like the 500 Cruiser #54125 or Chainsaw #50460)

Overall Length (with standard stock)

~43-44 inches (depending on stock configuration)

Capacity

5+1 rounds (6-shot tube magazine)

Performance and Use

Slug Accuracy: The rifled bore excels with sabot slugs (e.g., Remington Copper Solid or Hornady SST), delivering sub-MOA groups at 100 yards when paired with a scope. It's ideal for wooded areas where rifle calibers are restricted.

Versatility: Swap back to a smoothbore barrel for wingshooting. The 500A's dual extractors and twin action bars ensure reliable cycling.

Ergonomics: The synthetic or walnut stock (depending on model) includes a recoil pad. 

Historical Note: The 500A was produced from ~1961–1970 before evolving into the modern 500. Vintage models may have slight differences in markings or finish, but barrels remain interchangeable.

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