Medium machine gun
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.
[citation needed] 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.
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.
The heavy machine gun was mounted on a tripod and was often water-cooled; a well-trained and well-supplied crew could fire for hours on end.
In World War I, they were to be as important as the heavier designs, and were used to support squads and infantry on the move, on aircraft, and on many types of vehicle, including some tanks.
The lightest of the new designs were not capable of sustained fire, as they did not have extra cooling features and were fed from a comparatively small magazine.
Essentially a machine rifle with a bipod, weapons like the Chauchat or the Madsen 1902 were the most mobile, but were made for single and burst fire.
The Hotchkiss Mark I (e.g. Benét–Mercié M1909) was a 27.6 lb (12.2 kg) MG that normally used a mini tripod and linkable 30-round strips or in vehicles, but there was also a belt-fed version of it.
Not be confused with heavier Hotchkiss models (such as the M1914), the design proved a useful intermediate and would serve even to the end of World War II in some jobs.
The Lewis gun, which weighed 27 lb (12.3 kg), was commonly used with a 47-round drum and bipod; it was used on the move in support of squads, and on vehicles and aircraft as well, or on a tripod (either for anti-aircraft use, or to fill in for a heavier MG).
The French made a version of their infantry machine gun, the Châtellerault M1924, with 150-round magazine and internal water cooler.
The actual practice of using medium machine guns in different roles dates back to World War I, whatever the name given by different countries.
The trend toward replacing more types with mediums would receive a great boost as tactics using heavy water-cooled MGs were slowly phased out, but suffered a loss when there was shift back to lighter caliber automatic infantry support weapons.
They were similar in weight to an empty older light machine gun and several pounds lighter than mediums, but offered a much higher volume of fire due to their smaller caliber and lighter round; lower cartridge weight allows a greater total amount of ammunition to be carried by a gunner and/or other squad members carrying additional ammunition for the weapon.
Many models were scaled-down medium caliber designs or heavier, longer-barrel versions of infantry standard Assault rifles.
They essentially all have provisions for quick-change barrels and the ability to be fired from a bipod, tripod, or pintle mount, and weigh between 20-30 pounds.
