It will be difficult to find someone who has never seen six-barreled machine guns in a movie. They look pathetic and cool. Surely, everyone was curious at least once why this type of weapon has exactly six barrels. In order to understand this, one should turn to history, and also remember what happens to any firearm during firing.
From the point of view of military terminology, multi-barreled machine guns are considered weapons with a rotating cylinder block. The pioneer in this area was, of course, Richard Jordan Gatling, who in 1862 introduced his famous Revolving Battery Gun with six manually rotating barrels. The principle that the American engineer laid in his machine gun turned out to be so successful that it is still used today. The only difference is that the manual drive has long given way to mechanical and electrical, and the gravitational supply of ammunition (there was no spring in the stores for the Revolving Battery Gun and cartridges simply fell from above into the empty muzzle), gave way to modern machine-gun belts.
The design of the automatic cannon with a rotating block of cylinders today solves the same problems in the machine gun that it solved in the Gatling machine gun. As you know, when firing, a firearm emits a fairly large amount of heat, which is a by-product of the energy that is released when the gunpowder in the ammunition explodes. Gradually, the weapon and, in particular, its barrel heats up so much that it can jam.
This problem is especially relevant for machine guns. The issue can be solved by different methods. For example, if you look at the Lewis machine gun, you can see the characteristic shroud that provides better air cooling. Maxim's machine gun used water cooling. Modern machine guns are made of high quality materials that better dissipate heat. In addition, even modern machine guns use the "cooling" technique by quickly replacing the barrel of the weapon.
Multiple rotating barrels are another highly effective way to cool weapons. The essence of the method invented by Gatling is extremely simple. The loaded barrel fires, heats up, and then goes down, followed by a shot from the second barrel, which then also goes in a circle to cool. When the first fired barrel goes through a full rotation of 360 degrees, it is cooled by air quite enough so that with a new shot it does not cause the weapon to malfunction.
Modern six-barreled machine guns are cooled in the same way, the only difference is that thanks to the electric drive, they shoot much faster. Of course, the weapon still gradually overheats, but the presence of six barrels allows the Gatling machine guns to fire for a longer time, as well as create a better density of fire, compared to a similar single-barreled machine gun.
Continuing the topic DShK machine gun: a terrible weapon that can be disassembled with a hammer and cocked with the effort of two hands and not only.