+4 Magazine Extension Base Plate
Upgrade your reloads and grip with a durable +4 magazine extension designed to take a 17-round 9mm M&P magazine to 21 rounds while reusing the factory spring.
This extension was designed around the full-size M&P platform to provide a secure fit, added capacity, and improved handling without unnecessary bulk.
Compatible with 9mm M&P magazines only.
Why You’ll Want This
• Adds four additional rounds without changing springs
• Provides a more positive grip and seating surface
• Built for strength, reliability, and repeated use
• Clean, low-profile design that doesn’t feel oversized or awkward
Whether you’re setting up range mags, training mags, or duty-style spares, this extension adds capacity and confidence without compromise.
Product Details
The extension includes the extension body, internal spring guide, and locking tab, replacing the factory base plate entirely.
A 2.5 mm hex access hole is built into the design, allowing the locking tab to be tapped out if needed using either a 2.5 mm hex key or a small punch. This allows for clean, non-destructive disassembly if required.
No extra hardware is required.
Material
Made from PET-CF (carbon fiber reinforced PET) for excellent rigidity, dimensional stability, and heat resistance compared to standard plastics. This material was chosen specifically for functional performance, not appearance.
Fit & Compatibility
• Designed around full-size 9mm M&P magazines
• Works with compact models, though the extension will not sit flush with the grip
• Magwell compatibility is untested and not guaranteed
• Reuses the factory magazine spring
• Installs directly in place of the original base plate
Always verify smooth spring movement after installation.
Key Features
• +4 capacity increase (17 → 21)
• 9mm M&P compatibility
• Designed around full-size M&P
• Works with compact mags (non-flush fit)
• Durable PET-CF construction
• No extra hardware required
• 2.5 mm hex access for disassembly
Notes / Disclaimer
• Magazine and spring not included
• Magwell compatibility is not guaranteed
• This is an aftermarket accessory, not an OEM product
*Designed to fit OEM Smith & Wesson magazines ONLY*
Not for sale or shipment to states with magazine capacity restrictions.
