One of the most common questions I see from Benelli M4 owners is why their shotgun will only hold six rounds in the magazine tube, even after upgrading what they believe is already a “7-round” capacity configuration, either with a +2 magazine extension, or with a full 7 round tube swap.
In almost all cases, nothing is wrong with the shotgun, and this is how the shotgun is designed by Benelli. The issue comes down to ammunition variation and how tightly the system is already operating inside the available internal space inside the magazine tube.
The reality is, there is very little extra room inside the M4 magazine tube once the system is fully expanded for 7 round capacity. When you are trying to stack seven 2.75″ shells end to end, small differences in cartridge length become the deciding factor between 6 or 7 shells in the tube.
Not All 2.75″ Shells Are Actually The Same Length
Although ammunition is labeled as 2.75″, that measurement refers to the fired shell length, not the length of the unfired cartridge.
Unfired shell lengths vary quite a bit depending on manufacturer, hull design, payload, and crimp style. Roll crimps, fold crimps, buckshot loads, slug loads, and target loads all end up with different lengths usually based on the manufacturing process companies use.
During testing, I measured several common 2.75″ loads and found overall lengths ranging from approximately 2.26″ to 2.49″. That spread may not seem significant on paper, but inside a magazine tube, it adds up quickly.
Examples included:
- Target load: 2.26″
- Slug load: 2.30″
- 00 Buckshot: 2.32″
- Slug load: 2.36″
- 00 Buckshot load: 2.38″
- High brass buckshot: 2.49″
That is a variance spread of approximately 0.23″. When seven shells are stacked inside the magazine tube, those differences add up quick. A load measuring 2.26″ can easily fit seven rounds without issue, while a longer buckshot load measuring 2.49″ may only allow six rounds to be loaded.
This is completely normal limitation of the Benelli M4 platform, and is not a defect with the shotgun.
Roll Crimp vs Fold Crimp
Another factor is the type of crimp used by the manufacturer.
Some slug and buckshot loads use a roll crimp while many target loads use a fold crimp. Depending on the specific load and wad design, either style can result in a longer overall cartridge length. But the important takeaway is that two boxes of ammunition both labeled 2 3/4″ can occupy noticeably different amounts of space inside the magazine tube.
First, Make Sure You Actually Have A 7-Round Magazine System
First things first, it is important to confirm what magazine configuration your shotgun is actually running.
Many M4 and M1014 models come with a limiter from the factory. This configuration is limited to 5 rounds in the magazine tube. The OE magazine tube that is connected to the receiver on these models, is actually the same tube used in the Benelli M4 Entry 14″ SBS model. So to streamline the production line, Benelli uses this same Entry 5 round magazine tube on all models, and installs the limiter in the 18.5″ BBL models (like the civilian M1014). If the user wants to increase the capacity with an 18.5″ barrel, all they need to do is add a magazine extension by replacing the factory limiter.
This converts the 18.5″ BBL system into a proper extended configuration without requiring any permanent modification to the shotgun. A full 7-round tube replacement is also an option, but it requires removing the factory magazine tube from the receiver. This involves applying heat to break factory thread locker, and it is a completely doable modification, but it does carry a risk of damaging the receiver finish if done incorrectly.
The +2 Magazine Extension Ease Of Installation
Both options work, but our +2 extension is by far the easier installation. Installing a +2 extension simply involves removing the factory limiter and threading on the extension. See our Benelli M4 Magazine Extension Installation Guide.
No heat is required. No receiver disassembly is required. No risk of damaging the finish on the receiver.
For most owners, replacing the factory limiter with a quality +2 extension is the simplest and safest path to obtaining a true 7-round magazine system. With a properly machined +2 magazine extension, there is really no difference in performance between a +2 mag extension, or a full 7 round tube swap.
The Hidden Limitation
Even after upgrading to a true 7-round magazine system, some ammunition may still be too long to allow seven rounds to fit. The reason is simple.
Space inside the magazine tube is limited and every fraction of an inch matters. The factory spring retaining clip and magazine cap consume space that could otherwise be used by the magazine spring for additional capacity.
An Easy Way To Gain Additional Magazine Capacity
Our Titanium Magazine Cap was designed to optimize available magazine space.
When the internal spring retaining clip is removed while using our cap, it provides approximately 0.28″ of additional usable room inside the magazine tube. That additional space is often enough to make the difference between loading six rounds and loading seven rounds with longer buckshot or slug ammunition.
The same design is also incorporated into our Heat Shield Assembly, which utilizes a proprietary magazine cap that provides the same additional internal additional space.
For shooters trying to maximize magazine capacity without replacing ammunition or modifying the shotgun, increasing available internal volume is often the most effective solution.
Why We Don’t Add More Space Than Necessary
As mentioned above, our Titanium Magazine Cap adds approximately 0.28″ of additional usable internal space when the internal spring retaining clip is removed.
That number is intentional. The Benelli M4 magazine spring is designed around a specific compression range. While it is possible to create additional internal volume, doing so without any consideration for the engineering decisions Benelli has made, carries the risk of negatively affecting feeding consistency over time by reducing spring load.
Reliable function always comes first. The goal is not to maximize internal space at all costs. The goal is to recover just enough space to accommodate longer ammunition while as close as possible to the OEM spring design and maintaining proper operating compression.
This is also why the same design philosophy is carried through into our Heat Shield Assembly, which uses a proprietary magazine cap that provides the same controlled increase in internal space.
Final Thoughts
If your Benelli M4 will not accept seven rounds, the shotgun is usually not the problem. The most common culprit is variation in ammunition length.
First verify that your shotgun has been upgraded to a 7-round magazine system, then test the magazine with your preferred load out. In many cases, a small increase in usable magazine volume is all that is needed to reliably load seven rounds with longer defensive ammunition.