Medium machine gun

A medium machine gun (MMG), in modern terms, usually refers to a belt-fed automatic firearm firing a full-power rifle cartridge.

In the late 19th century, Gatling guns and other externally powered types, such as the Nordenfelt, were often made in different ranges of calibers, such as half-inch and one-inch. Thanks to their many barrels, overheating was not a major issue, and they were also quite heavy, being, essentially, heavy machine guns.

When Hiram Maxim developed his recoil-powered machine gun that used a single barrel, the first main design was a modest 26 pounds (11.8 kg) in weight, firing a .45-inch rifle caliber bullet (from a 24 inch long barrel). As depicted in a famous photo of Maxim, it could be picked up complete with its 15-pound (6.8 kg) tripod with one arm. It was similar to later-design medium machine guns, but it could not be fired for extended periods. As a result, he created a water-jacket cooling system to enable it to fire for extended periods. This added significant weight, as did changes to more powerful cartridges. This class of heavy, water-cooled machine gun would eventually be regarded as the classic heavy machine guns. However, the much lighter total weight possible by using recoil to power automatic loading was not lost on the firearms designers of the day, resulting in other automatic firearms that used this concept, such as the Borchardt pistol, the Cei-Rigotti rifle, the Madsen 1902, as well as lighter, gas-operated, air-cooled designs.

Many new designs were developed, some powered by air or recoil, or a combination of the two (e.g., the Colt 1895 and M1895, and the Hotchkiss). Also, instead of the rather heavy water jacket, new designs introduced other types of cooling, such as barrel replacement, metal fins, and/or heat sinks or some combination of all of them.

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