Comprehensive technical breakdown of Mossberg 500 and 590 shotgun platforms. Internal mechanisms, common variants, gunsmith service considerations, and professional maintenance procedures.
The Mossberg 500 and 590 series represent one of America's most successful shotgun platforms, with over 11 million units produced since 1961. Understanding the internal mechanisms, variant distinctions, and service considerations of these platforms is essential for professional gunsmith work, as these shotguns frequently appear in civilian, law enforcement, and military applications.
Core Platform Architecture
Both the 500 and 590 share fundamental design elements that define the platform's reliability and serviceability. The dual action bar system serves as the primary distinguishing feature from competitors like the Remington 870. These symmetrical action bars connect the forend to the bolt carrier, distributing operational forces evenly and reducing the likelihood of binding under adverse conditions.
The bolt system utilizes a rotating bolt head with dual locking lugs that engage barrel extension recesses. This positive lock-up provides strength for magnum loads while maintaining reliable extraction. The bolt carrier features an integral firing pin that strikes the primer through momentum transfer rather than spring pressure, eliminating a potential failure point.
Platform Variants and Specifications
The primary distinction between 500 and 590 models centers on magazine capacity, tube construction, and military specification features. The 590 incorporates a heavy-walled magazine tube with 8+1 capacity compared to the 500's standard 5+1 configuration. This enhanced tube construction withstands the increased stress of extended capacity and military use requirements.
| Component | Model 500 | Model 590 |
|---|---|---|
| Magazine Capacity | 5+1 (standard) | 8+1 |
| Trigger Guard | Polymer (typical) | Metal |
| Magazine Tube Wall | Standard thickness | Heavy-walled |
| Bayonet Lug | No | Yes (M9-style) |
| Barrel Options | 18.5" – 28" | 18.5" – 20" |
| Finish | Blued / camo | Parkerized / blued |
Field Stripping Procedure
Mossberg 500/590 field stripping requires no tools. Verify the chamber is empty and the action is open. Unscrew the magazine cap at the muzzle end—this releases the barrel. Pull the barrel forward off the magazine tube. The bolt and action bars can then be removed by cycling the forend fully rearward until the action bars disengage from the receiver tracks.
The trigger group assembly is retained by two pins through the receiver. Drive these pins from right to left using a 1/8" punch. The trigger group drops free as a complete unit. The elevator (shell carrier) is attached to the trigger group and should remain with it—do not attempt to separate them unless performing specific elevator service.
Common Service Issues
Shell carrier (elevator) spring breakage is the most common mechanical failure on both models. The carrier spring fatigues after extended service, causing shells to feed improperly or fail to rise into feeding position. Replacement requires removing the trigger group and separating the carrier from the trigger housing—a fiddly operation made easier with proper trigger group slave pins.
Action bar binding is a frequent complaint, particularly on aluminum-receiver versions. The bars can develop burrs or galling where they contact the receiver tracks. Polish the action bar contact surfaces with 400-grit followed by 600-grit abrasive to eliminate binding. Verify the forend moves freely before reassembling the barrel—a smooth cycling action is the verification standard.
The firing pin retainer pin on the 590 occasionally walks out under sustained firing. If a customer reports intermittent failures to fire with good primers, check the firing pin retainer pin position before condemning the firing pin itself. A retainer pin that has migrated allows the firing pin to ride forward under momentum and produce indented but unfired primers.