Installing a Benelli M4 magazine extension is one of the easiest and most popular upgrades for the platform. Unlike replacing the OEM magazine tube with a 7 round full tube, installing a +2 magazine extension (or +1 for Canadians) does not require heat, special tools, or removal of the factory 5 round magazine tube from the receiver.
The process is typically completed in just a few minutes and retains the Benelli M4’s factory “slip over the magazine” barrel removal capability (at least it does with the RX Arms magazine extension).
The video below walks through the complete installation process.
Summarized Installation Steps:
1. Verify the Firearm is Unloaded and SAFE.
Before beginning any work, ensure the firearm is unloaded and pointed in a safe direction. Always assume a firearm is loaded for safety reasons. Visually and physically inspect both the chamber and magazine tube to verify no ammunition is present.
2. Lock the Bolt to the Rear
Locking the bolt to the rear removes pressure from the barrel assembly and makes the installation process easier to complete.
3. Remove the Barrel and Handguard
Unscrew the magazine cap and remove the barrel assembly along with the handguard. Set these components aside for later.
4. Remove the Factory False Limiter
With the barrel removed, the factory limiter extension can be unscrewed from the front of the OEM magazine tube.
Many owners are surprised to learn that this component is not a true magazine extension. It simply limits the available magazine capacity while maintaining the appearance of a longer magazine tube.
5. Remove the Magazine Spring Retaining Ring
Carefully remove the internal magazine spring retaining ring with snap pliers. Watch out because that magazine spring may pop out and fly across the room, so best to try and keep it controlled and contained while you remove the spring retaining clip.
6. Optional: Reinstall the Retaining Ring Clip Inside the Extension
Some users prefer to install the factory spring retaining ring inside the end of the ID of the magazine extension. This is where tight tolerance maching comes into play. We machine our magazine extension to very tight tolerances to maintain retention ability of the spring retaining clip. If tolerances are too loose, this clip will not stay in place, and will slide over time.
Re-installing this clip allows the magazine spring to remain captured when the magazine cap is removed (when removing the barrel). If using this method, the spring must be compressed into the extension while threading the extension onto the OE magazine tube.
7. Install the Magazine Extension
If the retaining ring is not being reused, simply thread the magazine extension onto the end of the factory magazine tube. Hand tighten securely. No thread locker is required.
8. Reinstall the Barrel and Handguard
Reinstall the handguard and barrel assembly onto the firearm, loosely sliding the mid barrel ring, and front barrel ring over the newly extended magazine.
9. Install the Magazine Cap
Compress the magazine spring into the magazine tube and install the magazine cap. If you opted to use the spring retaining clip inside the magazine extension, then you can just simply screw on the magazine cap once the barrel is re-installed.
Tighten the cap hand tight.
You are now done and GTG.
Why Choose a Magazine Extension Instead of a Full-Length Tube?
While full-length tubes are certainly an option, replacing the factory 5 round magazine tube requires heating the receiver to soften the factory thread locker before removal. If excessive heat is applied, permanent cosmetic damage to the receiver finish can occur.
A +2 magazine extension avoids this process entirely and can be installed in minutes without specialized tools. For most users, it is the simplest path to a true extended-capacity magazine system.
Frequently Asked Questions:
Will the factory magazine spring work with the extension?
One of the most common questions I get asked. Yes. The factory spring is compatible with the full 7 round capacity tube. Benelli includes a spring that is compatible with both the 14″ Barrel Entry SBS, and the full length 18.5″ barrel.
Will I still be able to remove the barrel with the magazine extension installed?
Yes. Our design maintains the same “slip over the extension” barrel removal procedure as the factory Benelli M4 configuration. The barrel can be removed normally without removing the magazine extension. There are however other manufacturers out there whose design does not allow this, so be careful where you buy if this is important to you.
Does the magazine extension require thread locker?
No. The extension is designed to be installed hand tight.
Do I need to remove the factory magazine tube from the receiver?
No. The +2 extension (or +1 for Canadians) threads directly onto the existing factory magazine tube after removing the factory limiter extension.
Is a heat gun or propane torch required?
No. Unlike full-length 7 round magazine tube replacement, installing a magazine extension does not require heat.
Can I reinstall the factory limiter later?
Yes. The installation is fully reversible and the factory limiter extension can be reinstalled at any time if you so choose.
Will this increase my magazine capacity to 7 rounds?
Yes it will, but with a caveat. Different 2.75″ shells vary in overall length, which can affect how many rounds fit inside the magazine tube. Generally speaking, you should be able to get 7 rounds in the tube, but certain defensive shells are longer and may not fit 7 without adding a little more room. Something like our Ti Magazine Cap can fix this for you.
Why won’t my Benelli M4 hold 7 rounds after installing a magazine extension?
This is usually caused by ammunition length variation. Some buckshot and slug loads are significantly longer than others, even though they are all marketed as 2.75″ shells. You can get more info on this by reading our blog post: Why Won’t My Benelli M4 Hold 7 Rounds in the Magazine Tube?
Should I reuse the factory spring retaining ring?
If that is your preference, then go right ahead! Reusing the retaining ring inside the extension can make future disassembly easier by keeping the spring captured inside the extension body. But it does have the downside of reducing interior space for ammunition and may reduce your chances of getting 7 rounds in the tube.
Can the magazine extension loosen during use?
When properly hand tightened, loosening is uncommon. I recommend checking fit and function every time you take your gun out for shooting, and every time you are done for the day as a preventative measure.
Is a magazine extension easier to install than a full-length magazine tube?
Yes. Our magazine extension can typically be installed in a few minutes and does not require heating the receiver or removing the factory magazine tube.