In this video, Iraqveteran8888 talks about why some magazines are curved. Do you ever wonder why some of them kind of look like bananas and some of them look more straight? Where do magazines get their shape?
A 9mm has a pretty discernible taper to it, but some 9mm mags are relatively straighter, so it depends on the action that the magazine is going into and the way that the bullet picks up off of the magazine. With pistol caliber stuff, it comes down to grip angle.
If you look at Glock magazines, some of them have a particular angle to them. The cartridges feed right off, but as they stack in, they go at a bit of a backwards angle. They kind of stagger a bit and eventually end up as a single round on top. Glock magazines have a unique angle of grip. But then you look at a .45, it can get away with that because it’s a relatively non-tapered straight round. There might be a mild taper, but not enough to contend with. The grip can be straight because the magazine doesn’t need to be curved. To demonstrate, he used a Podavach tool.
Looking at a .30 carbine magazine, it’s perfectly straight, but compared to a later magazine that’s also a 30-round, there’s a discernible curvature. That’s because it’s a mildly-tapered round. The only way to overcome that taper is to curve the magazine so that the rounds don’t get jammed up in the magazine.
When you start comparing an AR-15 to an AK-47, it has a lot to do with the way the magazine locks into the gun. That’s one example of how the towers on the magazines and the design of the gun and the way it’s made to operate also contribute to the way the magazine is made.
In conclusion, there are a variety of factors that come into play when it comes to magazine shape.