What feature differentiates a medium machine gun from a light machine gun?

The feature that differentiates a medium machine gun from a light machine gun is primarily weight and portability. Medium machine guns are generally heavier, making them less portable and requiring a dedicated team for operation and setup. This increased weight allows them to fire larger caliber ammunition or sustain a higher rate of fire for extended periods compared to light machine guns.

Light machine guns, on the other hand, are designed to be more mobile and can be operated by a single soldier, making them suitable for supporting infantry in various combat scenarios. Their lighter weight facilitates easier transport and quicker repositioning on the battlefield, allowing for more tactical flexibility.

In terms of caliber size, while there can be differences, it is not solely definitive since some light machine guns can fire higher caliber rounds. The rate of fire can vary within both categories and is not a distinguishing feature as both types can have high or moderate rates of fire depending on the specific model. Cooling mechanisms, while present in both types, do not differentiate them significantly as design variations exist within both categories. Thus, weight and portability are the key factors that set medium machine guns apart from light machine guns.