Just playing Call of Duty and noticed the death machine spins and I always wondered why.
In: Engineering
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.
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