Just playing Call of Duty and noticed the death machine spins and I always wondered why.
In: Engineering
In simplest terms, firing at extremely high rates of speed creates a tremendous amount of heat. Firing that many rounds through one single barrel would likely Heat it to the point of very likely melt or distort the metal. By using multiple barrels, that distributes the heat over a wider range and prolong the life of the weapon. Second, it’s a simplified mechanism that allows the gun to operate at a high rate of fire while at the same time reducing extreme movement of the firing mechanism that would otherwise be required.
1. Shooting out of more barrels can increase the rate of fire. If you just had one barrel, it would be harder to achieve the same fire rate.
2. Heat. When you fire a gun, the barrel heats up. On machine guns, the barrel gets very hot with a continuous rate of fire. Increasing the number of barrels makes the barrels heat up slower since the bullets aren’t always being fired out of the same barrel.
Gatling guns had rotating barrels because it handled loading, ejecting the cartridge, and reloading the barrel. The innovation of ejecting the cartridge using exhaust gas hadn’t been developed yet. The Gatling gun was faster than a bolt-action gun.
More modern miniguns have multiple barrels to reduce overheating. Each barrel only fires a fraction of the shots, meaning you can fire more rounds before overheating.
Firearms with multiple barrels have the advantage of being able to fire for longer bursts as the heat build up is spread out. If a weapon is fired for too long the barrel can warp.
Machine guns do not spin; gatling guns do.
Bit of history: gatling guns were invented first. There are a couple problems with automatic weapons. The first is that you need to load the round into the barrel, and then you need to eject the spent cartridge. Gatling guns solved that by physically moving the barrel out of the way and having the mechanism tied to the rotation. It’s complicated to describe, but you can see an example in [these](https://i.imgur.com/t2Y75Gc.gif?noredirect) two [gifs](https://i.imgur.com/TmalWdB.gif).
In short, as the barrels are rotated, the cartridge drops down, is pushed into place inside the barrel, the hammer is pulled back, released, and then the cartridge is ejected. Neat! And *relatively* simple. The other problem, though, is that shooting a gun releases a lot of heat into the barrel. By having many barrels, the steel can be allowed to cool a bit between shots. The really neat thing about gatling guns is that you can shoot them as fast as you can rotate them, assuming you don’t melt the barrel. When they were first invented, this meant turning with a hand-crank. This will come up later.
Regardless, they need to rotate because the mechanism is tied to that rotation, and because the spent cartridge would still be in the way of the next cartridge coming in.
Machine guns use the recoil force from the cartridge firing to eject the spent cartridge, cock the hammer back, and load a new round. You can see that action in [this gif](https://thumbs.gfycat.com/HeartfeltImaginaryKiskadee-size_restricted.gif) (although the gun in this gif is *semi-automatic*, meaning the trigger has to be pulled between shots. A fully automatic weapon has a bit of extra mechanism to allow the hammer to release at the right time and fire the round).
Machine guns are mechanically much more complicated, requiring tight springs to shove the rounds back into place, and pretty tight machining to make sure everything fits the way it needs to. It wasn’t long after gatling guns were invented, but it still took a bit of work. Machine guns at the time could fire much faster than gatling guns, since you didn’t have to sit there and crank a thing. They’re also much lighter, since they only have one barrel. Overall, machine guns were mostly better.
And then someone had the terribly efficient idea of attaching a motor to a gatling gun. Why crank it when you can just use a motor? Less work and it’ll turn *way* faster. And then someone was like, motors are big, heavy, and have a max RPM. Why not use an electric motor instead, which will just keep going faster, and is lighter? And with that, modern gatling guns fire a *ridiculous* amount of bullets. You can see in [this video](https://youtu.be/NIJqbKXcSkA?t=280) what looks like a solid line of bullets. In actuality, those are just tracer rounds – bullets with a tiny bit of flammable material so they shine brightly, so you can see where the bullets are going. I don’t know for sure, especially with this gun, but my understanding is that tracers are loaded somewhere between every 7 to 12 rounds. So in the slow-mo of that gun firing, for each bullet you can [almost] see, there’s probably at least 7ish more that you can’t. Fun!
Gatling guns are still much heavier than machine guns, since they still have several barrels, *plus* some kind of motor to drive it. Thus, if you need to shoot a bunch of bullets from something you can carry, it’s almost certainly going to be a machine gun. If you need to empty an entire crate of ammo in under a minute, it’s going to be a gatling gun, almost certainly mounted to something like a vehicle.
When a gun fires a bullet, a lot of the explody gas heat energy transfers to the gun barrel; hot gun barrels can warp and deform which isn’t good. So a part of the reason you have multiple barrels is you can fire one barrel while 4 or 5 others are cooling down; by the time a barrel comes around to the active firing position again its cooled down enough. Also, a hot barrel might cause a round inserted in the breech to fire prematurely or explode or something. So cool barrels.
The other part is there is only so fast you can eject the spent shell casing and insert another shell casing into the breech of a gun. Attempting to do it faster with a single barrel+breech would cause the gun to jam. [Gatling guns are designed so a bullet is inserted and the casing ejected in numerous steps into each barrel as they rotate](https://www.youtube.com/watch?v=Yq6m7mpfc5A).
Guns heat up when they are shot. A lot. They get even hotter even faster when more bullets are fired. If they get too hot it can warp the metal in the barrel, which destroys the gun, or warp/melt the bullet, which makes it useless.
Most heavy machine guns are built with cooling systems in to disperse this heat. Getting guns, which fire too fast even for cooling systems, solve the problem by having multiple barrels. When the gun is fired, it’s only shooting one bullet at a time, but from a different barrel with every bullet, so the heat buildup is shared between multiple barrels instead of just one.
In the case of the gatling gun it has 5 barrels and one bullet is loaded and fired into each barrel then the spent casing is ejected and a new cartridge is inserted into the barrel and fired. This happnes with each barrell as it rotates and fires
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TLDR – Single barrel shoot fast, multiple spinning barrel shoot crazy fast (10x faster)
Gating guns and rotary cannons are distinctly different from machine guns
Your [standard machine gun](https://upload.wikimedia.org/wikipedia/commons/thumb/0/07/Browning_M2HB_Normandy.jpg/1280px-Browning_M2HB_Normandy.jpg) has a single barrel, a single breach, and does not spin.
Gatling guns spin so they can pull off stupid high rates of fire. A 6 barreled weapon like the [M134 Minigun](https://en.wikipedia.org/wiki/M134_Minigun) has basically 6 of everything – barrel, breach, and bolt. This duplication means that one barrel can be firing while a couple others are unloading and others are loading the next round and preparing to fire. Instead of having to make one gun that can fire, reload, and fire again extremely quickly ($$$), the duplication allows for each barrel to fire/reload much slower letting things be a bit cheaper and run a lot cooler. The reduced barrel temperature is more important for big guns like [the 20mm M61 Vulcan](https://en.wikipedia.org/wiki/M61_Vulcan) shooting 6000 rounds per minute
There are other spinning weapons like Revolver cannons which have a single barrel but duplicate the breach assembly so one round can be firing while others are loading/unloading. They can’t shoot as fast as a Rotary Cannon but they’re a lot lighter since they don’t have big spinning barrels. They’re less common because standard style completely non-spinning weapons are almost as good and easier to work with.
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