I have a question. Why no cartridges with a square (squircle) cross section? I don’t mean “why are cartridges cylindrical”, I’m more interested in why I’ve never seen one in the myriad weird and unconventional experimental cartridge types (like picrel). I get that cylinders can feed in any orientation and can double stack/double feed nicely, but is this rotational symmetry just a law of firearms or something? Or Is it just that there’s no need to deviate from a cylinder, or engineering hurdles that are a pain in the ass to tackle?

Reason for my question: a rounded square (corner radius = 1/4th the case diameter) increases case capacity by ~20% over a cylindrical case of equal diameter and length. This can come in handy if there are severe dimensional constraints on the cartridge, like if it going to feed through the grip. It can also be used to shrink the case head diameter and increase mag capacity (albeit only slightly) without affecting case capacity.