The discussion opens with a running joke about using the AK platform for every role before shifting into a more precise look at modular firearms. Modularity is described as more than just swapping a grip; it involves configuring a firearm for specific missions and environments. Examples include making a gun more compact for discreet or concealed carry, or larger and more obvious for outside-the-waistband use. The concept also extends to caliber configurability and the ability to adapt a single platform to home defense, concealed carry, vehicle defense, open carry, or trekking through the woods. This sets the framework for evaluating the top five most modular firearms based on how well they adapt to different roles and configurations.
The first pick is the Stoner 63, also known under designations such as M63, XM207, and XM23. Designed by Eugene Stoner, it was intended from the outset as a fully modular weapon system. The Stoner 63 could be configured as a top-fed light machine gun, an assault rifle, a carbine, or a belt-fed squad automatic weapon, all from the same core system. It saw service from the early 1960s to the early 1980s with both the U.S. Navy SEALs and the U.S. Marine Corps. Despite its versatility, the platform was mechanically complex and proved easier to damage or misuse in hard field conditions, which contributed to its relatively short service life, especially in Marine Corps use. The segment also notes that modern Next Generation Squad Weapon (NGSW) candidates continue this trend toward modularity to match changing mission requirements worldwide.
The number four pick is the ZEV Technologies OZ9, presented as a handgun built from the ground up for modularity. The example shown is an FDE Cerakote model. Its key feature is a central metal chassis with an integral Picatinny section that serves as the serialized firearm. Around this chassis, the barrel and slide form a second assembly, and the grip module forms a third. Users can swap grip modules for shorter or longer configurations, remove or change the beveled magwell, and choose between longer competition-style slides or shorter concealed-carry slides. The OZ9 accepts Glock magazines but offers a different feel, with a double undercut trigger guard, extensive stippling, and a more refined grip shape compared to an A2-style grip. The trigger performance and ergonomics are highlighted, and prior demonstrations at SHOT Show are referenced to illustrate how quickly the pistol can be reconfigured for more discreet or more openly carried roles.
The third pick is the AR-15 platform, represented by an IWI Zion pistol with a 12.5-inch barrel chambered in 5.56. While the original AR-15 was not especially modular, extensive aftermarket support and standardized parts have turned it into one of the most modular firearm platforms available. Users can perform caliber conversions to 300 Blackout, .50 Beowulf, .458 SOCOM, .22 LR, 9mm, .45 ACP, and others, typically by changing the upper receiver and appropriate components. Swapping uppers allows quick transitions between longer-distance setups and close-quarters configurations with shorter barrels, subject to legal restrictions on barrel length and rifle versus pistol classifications. A 16-inch intermediate setup can be converted into a short-barreled, close-quarters configuration or a longer-range option simply by changing uppers. Although not as simple as some systems that only require a barrel change, the AR-15 remains highly adaptable and caliber-convertible, which supports its reputation as one of the most modular firearms in the world.
The second pick is the SIG P320 series, which uses a modular chassis system similar in concept to the OZ9. The P320 can be configured as a compact or larger handgun by swapping grip modules, slides, and barrels. The serialized component is the internal metal fire control unit, not the external grip module. This allows a user to move the fire control unit between different grip sizes and slide lengths without purchasing a complete new firearm each time. The P320 platform, adopted by the U.S. military as the M17 and M18, benefits from strong aftermarket support, including chassis and brace systems from companies such as Flux Defense. These systems can add a brace or stock (where legally permitted), additional grips, and other accessories, effectively turning the P320 into a pistol-caliber carbine with extra points of contact. Owners can downsize a larger configuration for concealed carry by installing a shorter slide and more compact grip module, or scale it up for duty or home-defense roles, all while retaining the same serialized core.
Before revealing the top pick, an honorable mention goes to the Barrett MRAD, described as a Multi-Role Adaptive Design rifle. The MRAD is noted for its ability to switch between calibers such as .338 Lapua Magnum and 6.5 Creedmoor, along with other rifle cartridges suited to precision and distance shooting. Its modularity focuses on multi-caliber capability within the precision rifle role rather than broad mission types. Because the MRAD is dedicated to long-range precision applications, it is characterized as having essentially one primary role, despite its impressive adaptability within that niche. This narrower mission focus is given as the reason it does not fully make the main list, even though its caliber-changing system and design are recognized as technically advanced and highly modular for precision rifle use.
Loading... 
