Complete Mossberg 500 Shotgun Parts Diagram and Exploded View Guide
For precise disassembly or troubleshooting, refer to the exploded view on page 12 of the OEM manual (part number 92002, revision C). Key assemblies include the receiver group (components 401–423), bolt carrier (items 305–311), and tubular magazine (sections 260–285). The trigger mechanism (parts 150–172) and ejector (item 430) are critical for function–cross-check these against the annotated plate before adjustments.
Barrel lockup (component 240) must align with the rear lug (item 243) within 0.003 inches; use a feeler gauge to verify clearance. The operating handle (item 330) and its associated spring (part 332) require periodic lubrication with CLP-grade oil–apply sparingly to avoid fouling. For safety, confirm the tang safety (item 180) engages fully before field-stripping.
Aftermarket upgrades like extended magazines (verify thread pitch: 1/2″-20 UNF) or ghost-ring sights (mounting holes: #8-32) demand compatibility checks with the receiver rail (component 501). The forend tube (item 265) and action bars (parts 350–355) must move freely–inspect for burrs using a magnification loupe. Storage? Disassemble the bolt (components 305–308) and store with desiccant packets to prevent corrosion.
Electrical schematics aren’t applicable, but wiring harnesses for optics (e.g., red dot sights) follow standard 2-pin JST connectors. If modifying, solder joints should withstand 15A at 12V–use 60/40 rosin-core wire. For legal compliance, confirm any modifications adhere to BATFE 41P regulations, especially for pistol-grip stocks or barrel lengths under 18″.
Field-Stripping the Classic Pump-Action: A Hands-On Breakdown
Disconnect the barrel by unscrewing the magazine cap counterclockwise–no tools required. Rotate the cap until it separates from the tube, then slide the barrel forward and lift straight off the receiver. Check the chamber and ejector port for fouling before proceeding; excessive buildup here causes feeding failures in 870-style systems.
Depress the action release button (located directly behind the trigger guard) and pull the slide assembly rearward until it locks. Pinch the sides of the forend just ahead of the magazine tube, then tilt the assembly upward to disengage the lugs from the receiver tracks. The bolt will remain attached; grip the charging handle firmly and wiggle it free from the carrier rails.
Inspect the bolt face, extractor claw, and firing pin channel under strong light. Carbon deposits on the firing pin’s sides increase friction, causing light primer strikes. Scrub stubborn residue with a brass brush dipped in CLP–avoid wire brushes, as they erode the anodized finish. Reassembly reverses the order: mate the bolt to the carrier, align the forend lugs with the receiver grooves, then push forward until the action release button snaps into place.
Test function with snap caps before live ammunition. Cycle the action slowly, verifying the shell latch holds the carrier at full rearward travel. Stiff operation often indicates misaligned recoil spring coils–remove the buttstock and remove the spring, then stretch it 2–3 coils longer than factory specs to maintain proper tension after repeated compression.
Identifying the Pump Action Bar Group in Firearm Exploded Views
Examine the lower central region of the illustration where the sliding mechanism connects to the receiver. The action bar assembly appears as elongated, symmetrical components with distinct cutouts–often paired rods linking the forend to the bolt carrier. Look for numbering that references both the “bar link” and “action slide,” typically grouped near labels like “trigger housing” for spatial context.
Key identifiers include a rear crosspin securing the assembly and notched surfaces that interlock with the carrier. Older manuals may depict this part with dotted lines showing internal alignment, while newer versions use solid red highlights for clarity. The action bar’s front end should align with the tubular magazine’s mounting point in the diagram.
If the print uses color coding, the bar group usually shares tones with other moving parts (e.g., slide assembly) rather than stationary components. Compare against the parts list: terms like “action bar” or “pump linkage” will correspond to the drawn rods. Missing a single bar suggests a dual-rod setup; both must match length and curvature.
Forend removal drawings often isolate this assembly–verify bolt disengagement before handling. Damaged diagrams may obscure text; cross-reference adjacent sheets for consistent numbering. Some manuals split the bar group into “left/right links”–both halves must align perfectly during reassembly.
Detailed Component Guide for Pump-Action Shotgun Trigger Mechanism
Replace the sear spring first if the firing pin fails to reset–this part (#870-00-20) wears faster under heavy use than the hammer (#870-00-17). Inspect the trigger pivot pin (#870-00-21) for burrs every 500 rounds; file uneven edges to 0.005″ tolerance to prevent misfires. The disconnector (#870-00-24) should engage the hammer hook at a 45° angle–polish contact surfaces with 600-grit if reset feels sluggish. Keep the safety detent ball (#870-00-29) lubricated with dry-film grease; friction here causes 60% of accidental discharges during field stripping.
Prioritize the trigger bar (#870-00-23) during reassembly–ensure it rests flush against the receiver rail, with less than 0.01″ lateral play. The hammer strut (#870-00-18) must sit centered in its tunnel; misalignment here reduces pull weight by 2-3 lbs. Use a torque screwdriver to tighten the stock bolt (#870-00-33) to 18-22 in-lbs–over-torquing cracks synthetic stocks. Replace the extractor spring (#870-00-09) if case ejection becomes inconsistent; this 0.03″ wire coil fatigues faster than the larger ejector spring.
Locating the Magazine Tube and Follower in Firearm Assembly Illustrations
First, scan the exploded view for the elongated cylindrical part running parallel to the barrel assembly–this is the magazine tube. Verify its position against reference part numbers: typically labeled with a prefix like “MT” followed by sequential digits (e.g., MT-12). Confirm the tube’s length matches the firearm’s capacity specifications, as variants may differ. Misidentification risks confusing it with the forend or barrel nut.
Examine the follower next–the small, spring-loaded platform inside the tube. In illustrations, it appears as a flat or slightly curved piece with a central protrusion or notch. Compare it to adjacent components: the follower must align with the bolt’s feed path and interact directly with the shell lifter. Look for color-coding in newer manuals (often red or yellow) to distinguish it from similar parts.
| Component | Identifying Markers | Common Mistakes |
|---|---|---|
| Magazine tube | Cylindrical shape, labeled MT-xx, extends under barrel | Confused with heat shield or forend tube |
| Follower | Flat/curved with hole/notch, near spring | Overlooked as spacer or shell stop |
| Magazine spring | Coiled wire, elongates to 5-8x compressed size | Cut spring mistaken for recoil assembly |
Check the follower’s retention method. Some designs use a detachable collar or screw (visible in sectioned views), while others rely on friction from the tube’s crimped end. If the illustration shows a threaded cap, note whether it includes a witness hole for verifying spring tension. Failure to secure this component can lead to double-feeds or jams.
Trace the tube’s connection points in the diagram. One end should thread into the receiver (look for a hexagonal nut or ring), while the opposite end interfaces with the barrel nut or magazine cap. Many assemblies include a seal or O-ring at this junction–verify its presence, as missing seals cause gas leaks during cycling. Older iterations may lack these seals, necessitating aftermarket upgrades.
Inspect the spring’s representation. In exploded views, it’s drawn in an uncompressed state to illustrate full length, but actual installation requires careful compression. Look for arrows or annotations indicating rotation direction for threaded followers–incorrect threading damages the tube’s interior. Measure the spring’s wire gauge if replacing: standard sizes range from 0.8mm to 1.2mm, depending on firearm variant.
Cross-reference identified parts with the legend or adjacent numbered callouts. Poor-quality reproductions may omit critical details, so obtain source material from manufacturer-authorized manuals. For aftermarket modifications, confirm compatibility–some followers require milling or machining to match proprietary tube dimensions. Document all steps to avoid reassembly errors later.
Where to Locate Official Firearm Breakdown and Rebuild Guides
Begin with the manufacturer’s printed manual bundled with each pump-action shotgun. These booklets outline disassembly sequences in numbered steps, often accompanied by exploded-view illustrations. Current owners can request replacements directly from the maker’s website–search for “owner’s manual” under the specific model’s support section. Older manuals may exist as PDF archives on dedicated arms forums like AR15.com or Shotgun World, where enthusiasts upload scanned copies.
Trusted Third-Party Resources
- Brownells Gunsmith Tools & Videos: Their gunsmithing hub hosts free video walkthroughs that cover takedown and reassembly in real-time, paired with narration. Search for the model prefix plus “disassembly” for precise results.
- MidwayUSA Tech Pages: Visit their technical library; filter by brand to locate printable PDF guides, some exceeding 40 pages, with annotated photos for every sub-assembly sequence.
- YouTube: Channels like Hickok45 and FerFAL provide stripped-down tutorials–use timestamps in descriptions to skip directly to actionable steps.
For offline access, download GunData Pro or iGunPro apps; both include interactive teardown animations, parts lists, and torque specifications. DIY repair subreddits such as r/gunsmith frequently compile master threads linking verified sources–scroll pinned posts for curated lists avoiding paywalled or outdated content.