General Purpose Machine Guns

In our last couple of posts, we looked at medium machine guns. In today's post, we will look at some developments in the General Purpose Machine Gun (GPMG) category (otherwise called Universal Machine Gun or UMG).

A general purpose machine gun is a weapon designed to use both magazines and belt feed, firing full sized rifle-cartridges, which is air-cooled and designed to be used either as an infantry support weapon (i.e. like a light machine gun), or as a vehicle mounted weapon (i.e. like a medium machine gun). Since it is air-cooled, a GPMG usually features quick-change barrels, so it can continue to fire on automatic mode for longer periods of time. A general purpose machine gun can be mounted on a bipod or a tripod, or even from a vehicle, such as a jeep or a helicopter.

The first GPMGs were something we'd just studied in the previous post. The MG 34 was the first general purpose machine gun. Carried by an infantry man with a drum magazine and mounted on a bipod, it served as a great infantry support weapon used for offensive operations. By switching the magazine with an ammunition belt and mounting it on a tripod, it became a very good medium machine gun. Mounted on a tank or a vehicle, it was an effective anti-aircraft and defensive machine gun.

Public domain image of a MG 34 machine gun. Click on the image to enlarge

The only problem with the MG 34 was that it was somewhat harder to manufacture, due to the fact that it needed some precision machining. Due to this, the Germans came out with the MG-42, which was easier to manufacture, more reliable, and as an extra bonus, had a higher rate of fire as well!

A MG-42 mouinted on a tripod. Click on the image to enlarge. Public domain image.

The MG-42 design was extremely successful and some variants (such as the MG3 and MG74 models) are still in service in some militaries around the world. It also influenced other countries to manufacture their own GPMGs based somewhat on the MG-42 design.

The US military was one of the first to pick up the idea of a GPMG from the Germans and started working on a design in the late 1940s. One of the requirements was that this gun had to be chambered to fire 7.62x51 mm. NATO ammunition and another requirement was that it should be capable of being fired accurately from the shoulder as well. After a number of trials, the final design was approved in 1957 and was called the M60 machine gun. The M60 served in various branches of the US military during the Vietnam war. It was carried by infantry units as a Squad Automatic Weapon (SAW) to support infantry operations and was also mounted on river patrol boats (PBRs), M113 Armored Personnel Carriers (APC) and as a door gun on helicopters.

US Marines with a M60 in Vietnam. Public domain image.

While the M60 saw service in Vietnam, some design flaws became obvious. For one, it had some jamming issues in muddy and humid conditions. It did better when used in static-defense or helicopter mounted roles, because it could be stored in cleaner conditions and regularly maintained. One more problem was the design of the barrel, which had a permanently attached bipod and this made barrel changes more difficult and took longer to accomplish. While some improvements to the design were made, the US military rejected the M60E3 and went with the Belgian FN MAG (which we will study in a second) and designated it as the M240 in US service.

Around the time that the US was developing the M60, the Fabrique Nationale company (FN) of Belgium was also developing their own GPMG, which they called the FN MAG (the letters MAG stood for Mitralleuse d'Appui Generale, which is French for "General Purpose Machine Gun"). Like the M60, the FN MAG is also designed to fire 7.62x51 mm. NATO cartridges. While it is heavier than the M60 and uses a more complicated gas operated system, it is more reliable compared to the M60. This is why it was also adopted by the US military as the M240 to replace the M60s in service. The M240 was first mounted on to tanks in 1977 and later adopted by other US military branches during the 1980s and 1990s.

US Marines firing a M240G mounted on a tripod. Click on the image to enlarge. Public domain image.

The FN MAG and the M240 continue to be used in service in many military forces around the world.

Other GPMGs include the Soviet PK series, the Heckler & Koch HK 21 etc.

Medium Machine Guns - I

In our last few posts, we looked at light machine guns and heavy machine guns. Briefly, a light machine gun fires intermediate-sized ammunition, comes with a bipod, operated by a single user and is generally carried by and used to support infantry. A heavy machine gun fires larger-than-ordinary rifle cartridges, is mounted on a vehicle or a tripod, sometimes operated by a team of people and is used against troops, light armor, buildings, low flying aircraft etc. In today's post, we will study another class of machine guns, the medium machine gun, otherwise called the MMG.

A medium machine gun is a weapon that fires full-sized rifle cartridges in automatic mode. They are generally air-cooled and belt fed. They also weigh somewhere in between the weight of a light machine gun and a heavy machine gun. Typical weight for a MMG is somewhere between 25 lbs. and 40 lbs. (or 11.34 kg. to 18.14 kg.) They began to emerge towards the end of World War I, as a balance between light machine guns and heavy machine guns. Recall that in World War I, light machine guns were made to be fed by smaller box magazines and fired in bursts only. Medium machine guns were designed to be fired on automatic for much longer, but without the heavy water cooling mechanism, weight or recoil of a heavy machine gun. Therefore, a medium machine gun offered flexibility to be used with a bipod by infantry like a light machine gun, or mounted on a heavier tripod or vehicle and used similar to a heavy machine gun. For this reason, a medium machine gun is sometimes referred to as "General Purpose Machine Gun (GPMG)" or "Universal Machine Gun".

The first real MMG was the Browning designed M1919 medium machine gun. This is a weapon that fires .30 caliber rifle cartridges from an ammunition belt. It was designed as an air-cooled variant of the M1917 heavy machine gun. Unlike the M1917 which weighs 103 lb. (47 kg.), the M1919 only weighs 31 lbs. (14 kg.) The minimum number of people needed to operate it is two, but sometimes upto four people were involved: a gunner (who fired the gun and also carried the tripod and some ammunition, when moving the gun), an assistant gunner (who fed the ammunition and carried the gun, when on the move) and two other people to carry extra ammunition, barrels, tools etc.

US Marines operating a M1919 A4 during World War II. Click on the image to enlarge. Public domain image.

This weapon was heavily used in World War II by different branches of the US military. It was used by infantry troops, mounted on jeeps, tanks, armored personnel carriers, aircraft etc. and continued to be used well into the Vietnam era. It was also used by other military forces around the world and modified to take other rifle cartridge calibers as well, such as .30-06, 7.62x51 NATO, .303 British, 7.62x54 mmR etc. In fact, it is still in use in some parts of the world.

In our next post, we will look at some more medium machine guns.

Machine Guns - General

In our last few posts, we studied different feed systems such as ammunition belts, chain feeds and feed strips. All these mechanisms are generally used with machine guns. Therefore, in the next series of posts, we will study all about machine guns.

A machine gun is a firearm that is capable of fully automatic fire. What this means is that as long as the firearm has ammunition available to it and the trigger is pulled, it will continue to load and fire ammunition automatically. Machine guns are capable of firing at high rates of several hundred rounds per minute and are designed to keep firing for considerable periods of time. The capability of maintaining sustained fire for long periods of time is what distinguishes a machine gun from an automatic rifle or an assault rifle (both of which can fire on full-auto only for limited periods of time).

US military doctrine has another interesting way of classifying automatic rifles versus machine guns. If the fully automatic firearm is operated by a crew, then it is a machine gun, but if a fully automatic firearm is operated by a single person, then it is an automatic rifle. In many cases, weapons fall exclusively into one of these two designations, however, we have one major oddball that falls into both categories -- the M249. US Army Field Manual FM 3-22.68 ("Crew-Served Machine Guns") describes the M249 as both an automatic rifle and a machine gun! Quoting from the manual chapter 4, section 5, paragraph 4-207, "Both the M249 automatic rifle and the M249 machine gun are identical, but its employment is different. The M249 automatic rifle is operated by an automatic rifleman, but its ammunition may be carried by other Soldiers within the squad or unit. The M249 machine gun is a crew-served weapon."

Machine guns can be portable as well as mounted and therefore, they are generally classified based upon size.

Before we dig deep into the topic, let us talk about submachine guns, which are portable firearms that are designed to fire pistol-sized ammunition. While they have a high rate of fire, some authorities do not consider these as "true machine guns" as they are not capable of sustained fire for long periods of time. Examples of these would be the Thompson submachine gun (which actually coined the term "submachine gun") also known as the Tommy gun, Chicago typewriter, Trench broom etc., Heckler & Koch MP5, Uzi etc. All these weapons are designed to fire pistol sized ammunition such as .45 ACP, 9 mm Parabellum etc.

Next, we have true machine guns like the Light machine gun, Medium machine gun, Heavy machine gun, General purpose machine gun which all use larger ammunition calibers (rifle calibers or larger). These weapons are generally heavier than other automatic weapons (even the "light" machine gun is heavier than an assault rifle, for instance). Examples of these would be the Lewis gun, the Bren gun, MG-34, Browning M1917, Browning M2, M60 etc.

A Lewis gun. Click on the image to enlarge. Public domain image. 

A M60 machine gun. Click on the image to enlarge. Public domain image.

We will study more into these various types of machine guns in the following posts.

Finally, we have weapons in the autocannon category. The difference between an autocannon and a machine gun has largely to do with the type and size of ammunition. If the firearm uses ammunition greater than 16 mm. diameter, or if it uses large caliber explosive rounds, then it is considered an autocannon rather than a machine gun. Examples of an autocannons include the M242 Bushmaster (which we studied briefly, when recently studying about chain guns), Oerlikon 20 mm. autocannon etc.

Since machine guns are designed to fire on automatic for longer periods of time, they tend to overheat quickly. Hence, many of them are either designed to have a built in barrel cooling system or feature a quick-change barrel replacement system. For the same reason, most machine guns are also designed to fire from an open-bolt, so that the breech area can be more efficiently air-cooled when the gun is not firing.

In the next few posts, we will study all about various types of machine guns and their history.