Yup, from what I've seen, the pretty ones are nice and round and smooth, and the mid-war ones tend to have a flat spot about there. It was probably a machining method that got turned from 'make it nice and round' during peacetime to three stages during war. Curve one side, the other, smooth it off.
My guess is that, at some point, "Here's some good ammo, follow the guy with the rifle" turned into "Here's some rusty rounds, follow the guy throwing rocks" and they stopped paying much attention to Step #3.