CMMG, Inc Magazine Extension Kit, Five-seveN Pistol, 10rd Review

Getting Up Close with the CMMG, Inc Magazine Extension Kit, Five-seveN Pistol, 10rd

As a gear and equipment specialist with over a decade of putting tools through their paces in everything from dusty workshops to rigorous field tests, I approach new products with a healthy dose of skepticism and a keen eye for detail. My quest for optimizing firearm capacity, particularly for the FN Five-seveN, led me to the CMMG, Inc Magazine Extension Kit, Five-seveN Pistol, 10rd. The promise of a simple, non-permanent way to increase magazine capacity is always appealing, especially for a pistol known for its unique caliber and handling. I was hoping this kit would offer a practical solution to extend its utility without compromising reliability.

I acquired this CMMG extension kit after a few range sessions where the standard magazine capacity of my Five-seveN felt a bit limiting for longer training periods. While I considered a few aftermarket options, the CMMG offering stood out for its stated ease of installation and the fact that it didn’t permanently alter the factory magazine. My initial impression upon unboxing was one of functional simplicity; the parts themselves are straightforward, and the plastic feels durable enough for its intended purpose. It’s a fairly basic piece of equipment, but sometimes, that’s exactly what you need.

My immediate reaction was one of cautious optimism. The kit looked like it would do the job, but the user feedback I’d seen online hinted at potential complications. I was eager to see if my hands-on experience would align with those mixed reviews or if the CMMG extension would prove more robust in practice.

Real-World Testing: Putting CMMG, Inc Magazine Extension Kit, Five-seveN Pistol, 10rd to the Test

First Use Experience

My initial testing of the CMMG, Inc Magazine Extension Kit, Five-seveN Pistol, 10rd took place at my local indoor range, a controlled environment where I could meticulously observe its function. The installation process, as advertised, was indeed quick; it involved removing the factory floor plate, sliding the extension on, reinserting the spring, and reattaching the floor plate. I performed this on two factory FN Five-seveN magazines.

The extension kit integrated onto one magazine without a hitch, fitting snugly and appearing to be a solid unit. However, on the second magazine, I encountered a slight issue where the plastic of the extension seemed a bit misaligned with the factory base of the magazine, requiring some firm pressure to seat. While it eventually locked in, this minor discrepancy immediately raised a small flag regarding manufacturing tolerances.

When loading rounds into the modified magazine, the difference in feel was noticeable. The spring seemed to exert a bit more tension towards the end of the travel, which is to be expected with a longer follower path. The true test, however, came when I went to shoot.

Extended Use & Reliability

After several range sessions and approximately 150 rounds through the modified magazines, a pattern of inconsistency emerged, mirroring some of the user feedback I’d encountered. While the magazines would function adequately for the first 5-7 rounds, beyond that point, particularly when loaded closer to the advertised 10-round capacity, I experienced feeding issues. Specifically, the follower would sometimes fail to keep pace with the descending rounds, leading to a failure to feed.

This necessitated a complete disassembly of the magazine to reseat the follower and spring correctly. This interruption significantly disrupted the flow of shooting and training, turning what should be a seamless extension into a frustrating point of failure. I found myself reverting to the factory magazines for reliable performance during any sort of timed drills or prolonged shooting.

The durability of the extension itself seemed adequate, with no visible cracks or structural damage despite being handled repeatedly and subjected to the recoil of the pistol. However, the functional reliability after the follower entered the extended portion of the magazine was a significant concern. Maintenance was straightforward, as it essentially involved disassembling and reassembling the original magazine, but the recurring need to do so negated any perceived benefit. Compared to the flawless operation of the factory magazines, this extension kit fell considerably short, failing to provide the expected boost in capacity without introducing significant reliability problems.

Breaking Down the Features of CMMG, Inc Magazine Extension Kit, Five-seveN Pistol, 10rd

Specifications

The CMMG, Inc Magazine Extension Kit, Five-seveN Pistol, 10rd is designed to modify the factory FN Five-seveN pistol magazine, increasing its capacity. The kit includes the extension housing and a chrome silicon spring. This spring is specifically noted as being salt water resistant and designed to not take a set, meaning it should maintain its tension over time.

The primary specification this kit addresses is magazine capacity, aiming to bring a standard Five-seveN magazine up to a 10 round capacity. The materials used appear to be durable polymer for the extension body and steel for the spring. The finish is a simple Black to match most firearm components.

The inclusion of a chrome silicon spring is a good detail, as it offers better resilience against corrosion and maintains its spring rate more effectively than standard springs. This is important for consistent feeding over many cycles. However, the advertised 10 round capacity is where the primary functional challenge lies, as my testing revealed that achieving this reliably is problematic.

Performance & Functionality

The core function of this extension kit is to provide increased ammunition capacity. In theory, it should seamlessly integrate with the factory magazine, allowing the follower to travel further up the extended body, thus accommodating more rounds. The CMMG extension, when installed, does physically allow for additional rounds to be inserted.

However, its performance suffers significantly beyond the original magazine’s capacity. The primary issue lies in the follower’s ability to navigate the transition from the factory magazine body to the extension. It appears that the follower can snag or fail to track properly within the larger volume of the extension, leading to feeding malfunctions.

This means that while it might hold more rounds, it cannot reliably feed them. The product barely meets expectations in terms of simply holding more ammunition, but critically fails in its essential function of reliable feeding. The advertised 10 round capacity becomes a theoretical maximum rather than a practical one.

Design & Ergonomics

The design of the CMMG extension kit is quite utilitarian, focusing on functional addition rather than aesthetic refinement. The black polymer construction aims for a blend with the factory magazine, and it does a decent job of looking like a natural extension of the original component. The shape is largely a simple cylindrical or slightly tapered tube that continues the lines of the factory magazine base.

Ergonomically, once installed, the extension does make the magazine slightly longer, which can offer a bit more surface area for the hand to grip. However, this slight increase in length can also impact concealment and the smooth drawing of the pistol if it catches on clothing or holsters. The main ergonomic drawback arises from the unreliability; the need to frequently disassemble the magazine negates any positive ergonomic feel.

The fitment, as noted, can be a minor issue, with slight variations in plastic molding potentially causing a less-than-perfect lock-up. While it doesn’t permanently alter the magazine, the need for forceful seating on one unit suggested a less-than-ideal manufacturing tolerance.

Durability & Maintenance

The CMMG extension kit, in terms of its physical structure, appears to be reasonably durable. The polymer material used for the housing is thick enough to withstand the stresses of insertion and removal from the firearm. The chrome silicon spring also bodes well for long-term tension and corrosion resistance, which are key aspects of magazine reliability.

Maintenance of the kit is, in essence, the maintenance of the factory magazine it modifies. This involves periodic disassembly, cleaning, and inspection of the follower, spring, and magazine body. The extension itself requires minimal cleaning, typically just a wipe-down to remove dust or debris.

The primary concern regarding durability isn’t physical wear and tear, but rather the functional lifespan of the system when pushed beyond its intended design limits. The feeding issues suggest that the inherent design might not be robust enough to handle the increased spring tension and follower travel required for the higher capacity, potentially leading to premature wear on the follower or spring engagement points. There is a risk that repeatedly forcing it to function at 10 rounds could lead to faster degradation of the follower’s ability to track correctly.

Accessories and Customization Options

The CMMG, Inc Magazine Extension Kit, Five-seveN Pistol, 10rd is essentially a single component designed to enhance an existing factory part. It does not come with additional accessories. The kit itself is the customization option for your FN Five-seveN magazine.

There are no other customization options directly related to this specific CMMG product. Its purpose is singular: to add capacity. It is designed to work with the factory FN Five-seveN magazine and does not offer compatibility with aftermarket magazine bodies or modifications. The chrome silicon spring is an integral part of the kit, providing the necessary tension for the increased capacity.

Pros and Cons of CMMG, Inc Magazine Extension Kit, Five-seveN Pistol, 10rd

Who Should Buy CMMG, Inc Magazine Extension Kit, Five-seveN Pistol, 10rd?

This CMMG, Inc Magazine Extension Kit, Five-seveN Pistol, 10rd is suited for FN Five-seveN owners who are looking for a potential capacity increase and are willing to accept a compromise in reliability. It might be considered by those who value the ability to load a few extra rounds for specific, non-critical scenarios where a minor feeding hiccup is acceptable. Hobbyists who enjoy experimenting with firearm modifications and have the patience for troubleshooting might find some interest.

However, I would strongly advise against this product for anyone who relies on their firearm for duty, self-defense, or competitive shooting where absolute reliability is paramount. Law enforcement officers, competitive shooters, or individuals who need a dependable firearm for personal protection should absolutely avoid this kit. Those who require consistent performance and do not want to deal with frequent magazine disassembly should stick with factory magazines. If you are looking for a simple, trouble-free capacity increase, you would be better served by exploring other platforms or manufacturer-specific solutions if they exist.

Conclusion on CMMG, Inc Magazine Extension Kit, Five-seveN Pistol, 10rd

My experience with the CMMG, Inc Magazine Extension Kit, Five-seveN Pistol, 10rd has been disappointing, primarily due to the significant reliability issues that emerge when attempting to reach its advertised 10 round capacity. While the kit is easy to install and utilizes seemingly durable materials, including a resilient chrome silicon spring, its core function is severely hampered by feeding malfunctions. The follower simply doesn’t track reliably within the extended portion, turning what should be a simple capacity upgrade into a source of frustration.

For its price point, approximately $26.59, one might expect a more seamless integration and reliable performance. However, the issues I encountered, along with similar feedback from other users, suggest that this extension kit compromises the fundamental reliability of the FN Five-seveN magazine. While it does offer a non-permanent way to hold more rounds, it fails to deliver them consistently.

Ultimately, I cannot wholeheartedly recommend the CMMG, Inc Magazine Extension Kit, Five-seveN Pistol, 10rd for anyone prioritizing dependable firearm function. If you are looking to simply experiment or are willing to accept the trade-off in reliability for a few extra rounds in very specific, non-critical applications, it might be a consideration. However, for most users, especially those who depend on their sidearm, sticking with the flawless performance of the factory magazines is the far wiser choice.