Modularity can provide several advantages to military organizations, such as the versatility of allowing units to quickly tailor their weapons to best suit the immediate tactical needs, to quickly repair/exchange malfunctioned components, and to reduce overall logistical burdens and costs.
However, it also make the legal tracking and technical categorization of a weapon more complicated as it can now be easily converted into a diverse variety of different forms.
[1] For example, the Stoner 63 is a 5.56×45mm NATO-caliber modular small arm system using a variety of modular components, which can be configured as a rifle, a carbine, a top-fed light machine gun, a belt-fed squad automatic weapon, or a vehicle mounted weapon.
A modular firearm can also be useful for hunters, which then easily can change to a different chambering or barrel length when hunting different species.
These systems simplify the replacement of worn barrels or caliber changes, since they often only require the use of a hex key, thus eliminating the need for special tools and custom fitting by a gunsmith.