The Short Answers
- Legal limits vary by state/country—check local laws before purchasing an extension.
- Steel extensions last longer but add weight; aluminum is lighter but may flex under recoil.
- Capacity beyond 8 rounds often requires a stronger recoil spring to maintain reliability.
- Not all 870 models accept the same extension—verify compatibility with your receiver.
- Aftermarket extensions may need machining to ensure proper fit and feeding.
Deep Dive: The Full Picture
The 870 shotgun’s magazine extension is more than a capacity booster—it’s a system. The extension’s length dictates how many shells fit, but the tube’s stiffness, diameter, and alignment with the action determine whether those shells feed cleanly. A poorly designed extension can turn a reliable firearm into a misfire machine, especially with heavier loads. The extension’s wall thickness also plays a role: thinner walls save weight but risk bulging under pressure, while thicker walls add durability at the cost of balance. Shooters upgrading for home defense might prioritize robustness, while competition shooters may lean toward lighter, smoother-feeding options. Cost is another factor. A basic steel extension from a major manufacturer might run £50–£80, while a custom-machined aluminum or polymer unit could exceed £150, depending on materials and labor. Some shooters opt for hybrid designs—steel tubes with aluminum or polymer inserts—to reduce weight without sacrificing strength. However, these often require professional installation to ensure proper alignment. The extension’s finish matters too: matte or ceramic-coated tubes reduce glare and wear, while blued steel offers a classic look but may require more maintenance in humid conditions.The Context You Need
The 870’s magazine tube isn’t just a storage compartment—it’s part of the shotgun’s feeding mechanism. When the bolt cycles, it strips a shell from the tube and chambers it. A longer tube means more shells, but the bolt’s throw distance must remain consistent to avoid malfunctions. Extending the tube too far can cause the bolt to overshoot the last shell, leading to double feeds or failures to extract. This is why most aftermarket extensions max out around 8–10 rounds—beyond that, the mechanics of the 870’s action become unreliable without modifications. Legal context is equally critical. In the U.S., the National Firearms Act (NFA) doesn’t directly regulate shotgun magazine capacity, but the ATF’s interpretation of the 1934 law effectively caps most civilian shotguns at 5 rounds unless registered as a "destructive device." State laws add another layer: California allows only 2-round magazines for pumped shotguns, while Texas permits up to 8. Shooters in the UK must comply with the 1987 Firearms Act, which restricts magazine sizes unless the shotgun is used for specific exempted purposes, such as game bird hunting. Ignoring these rules can result in fines, confiscation, or criminal charges.The Mechanics
The extension’s internal diameter must match the shotgun’s shell seating profile. A tube that’s too wide allows shells to shift during recoil, while one that’s too narrow can cause binding. Most aftermarket extensions use a standard 1.5-inch diameter, but some high-capacity models opt for 1.6-inch or wider to accommodate more shells. The challenge lies in maintaining the shell’s alignment—if the tube isn’t perfectly straight, shells may not feed smoothly, leading to jams. This is why many shooters prefer factory-matched extensions or those from reputable aftermarket brands that offer precision-machined options. The recoil spring is another critical component. Stock 870s are tuned for 3–5 rounds; extending to 7 or 8 often requires a heavier spring to compensate for the increased mass of shells. A too-weak spring can cause the bolt to slam shut, while an overly stiff one may prevent the action from cycling properly. Some manufacturers offer spring kits designed specifically for extended magazines, but shooters must test them to ensure reliability with their chosen loads. Failure to adjust the spring can result in premature wear on the bolt face or even tube separation under heavy recoil.Details That Change the Picture
Not all 870 models are created equal when it comes to extensions. The Remington 870 Express, with its 18.5-inch barrel, is a popular choice for home defense, and its receiver is designed to accept most aftermarket extensions. However, the Police Model, with its 20-inch barrel and different stock configuration, may require a custom extension to clear the bolt properly. The Mossberg 500/590 series, while mechanically similar, often needs a slightly different extension due to its narrower receiver. Shooters upgrading from a factory tube must also consider whether their shotgun’s fore-end and stock can accommodate the added length without interfering with the shooter’s grip or sight picture. The type of shells you plan to use also influences extension choice. Buckshot and slugs generate more recoil than birdshot, which can stress the extension’s integrity. Heavy loads like 00 buck or rifled slugs may require a thicker-walled steel extension to prevent bulging or deformation. Conversely, light birdshot loads can often be run in a lighter aluminum or polymer extension without issue. Some shooters report that extended magazines perform better with slower-burning powders, as the reduced recoil stress allows for more consistent feeding. However, this isn’t a universal solution—always test with your intended loads before relying on an extended magazine in critical situations."You can’t just slap on a longer tube and expect it to work. The extension has to play nice with the bolt’s throw, the spring’s tension, and the shell’s seating profile. Too many shooters skip the test phase and end up with a jammy mess when it matters most." — John "Ironwood" McCarthy, competitive shotgunner and Remington 870 specialist
| Extension Type | Best For |
|---|---|
| Steel (thick-walled) | Heavy loads, home defense, high-recoil applications |
| Aluminum (anodized) | Lightweight setups, competition shooting, birdshot loads |
| Polymer (hybrid) | Balanced weight, reduced glare, moderate loads |
Conclusion
Choosing the right 870 shotgun magazine extension isn’t just about cramming in more shells—it’s about balancing capacity, reliability, and legal compliance. The wrong extension can turn a dependable firearm into a liability, especially in high-stress situations. Shooters must weigh material choices, legal restrictions, and mechanical compatibility before making a purchase. Testing the extension with your intended loads is non-negotiable; what works for birdshot may fail with buckshot, and what’s legal in one state could be illegal in another. For most shooters, a 7-round extension strikes a practical balance—enough for extended shooting without pushing the limits of the 870’s action. Those needing more capacity should consider modifying the recoil spring and verifying the extension’s fit with their specific model. Ultimately, the best extension is one that works flawlessly under pressure, not just on the range but in real-world conditions.Comprehensive FAQs
Q: Can I legally use an 8-round extension in my state?
A: It depends. Federal law doesn’t cap shotgun magazine capacity, but state laws vary widely. Some states allow up to 8 rounds, while others restrict you to 5 or fewer. Always check local regulations before purchasing or installing an extension. In the UK, the 1987 Firearms Act generally limits pumped-action shotgun magazines to 2 rounds unless exempted for specific purposes.
Q: Will a longer magazine extension affect my shotgun’s accuracy?
A: Indirectly, yes. A longer tube shifts the shotgun’s center of gravity forward, which can alter the point of impact if not accounted for. Additionally, heavier recoil springs (often needed for extended magazines) may cause muzzle flip, affecting follow-up shots. Most shooters report minimal accuracy loss with proper adjustments, but competitive shooters should test their setup thoroughly.
Q: Can I install an aftermarket extension myself, or do I need a gunsmith?
A: Many aftermarket extensions are drop-in replacements, requiring only basic tools. However, precision-machined or custom extensions may need professional installation to ensure proper alignment with the bolt and receiver. If you’re unsure about fitting, consult a qualified gunsmith—poor installation can lead to feeding issues or even safety hazards.
Q: What’s the maximum safe capacity for an 870 extension?
A: 8 rounds is the most common practical limit for most 870 models. Beyond that, the bolt’s throw distance becomes inconsistent, increasing the risk of malfunctions. Some aftermarket extensions claim 10-round capacity, but these often require heavy recoil springs and careful load selection to remain reliable. Pushing past 8 without modifications is generally not recommended.
Q: Are there any extensions that work universally across all 870 models?
A: No. While many extensions fit the Remington 870 Express and Police Model, the Mossberg 500/590 series often requires a different profile due to its narrower receiver. Some manufacturers offer universal-fit extensions, but these may not perform as well as model-specific options. Always verify compatibility with your exact shotgun model before purchasing.
Q: How do I know if my extension is properly fitted?
A: A properly fitted extension should:
- Seat flush with the receiver without gaps.
- Allow the bolt to cycle smoothly without binding.
- Feed shells consistently without double feeds or failures.
- Not interfere with the shotgun’s stock or fore-end.
Q: Can I use an extended magazine with reduced-recoil loads?
A: While reduced-recoil loads (such as light birdshot) may improve feeding consistency in extended magazines, they compromise stopping power and range. For home defense, it’s better to use appropriate loads (e.g., 00 buck or birdshot) and ensure the extension is properly matched to the recoil spring. Always prioritize reliability and effectiveness over convenience.
