| Because there's a ton of organic growth over more than a century and a shitton of holdovers. Think of it like really old legacy systems in computing. Like look just at naming: old stuff was often named based on caliber and the number of grains of powder back in black powder days. Like the .45-70 is a .45 bullet and had 70 grains of black powder in a standard load. But then this carried over when they named the .30-06, which had a .30 bullet and 6 grains smokeless. Some handgun rounds are "ACP" because they were developed for new (at the time) auto-loaders instead of revolvers. Now cartridges are mostly named by caliber. Then there's stuff where cartridges were slightly tweaked, like for NATO. .223 is mostly the same as 5.56 and .308 is mostly the same as 7.62, but the latter are both NATO rounds re-named and changed a bit from their predecessors. Oh and by the way, .308 rifles can typically fire .308 or 7.62, it's not safe to fire .308 from a 7.62 rifle though. Oh but for .223/5.56 it's the other way: You can fire .223 from a 5.56 chamber but not vice versa. Every country developed its own rounds for a long time, just look at the number of 9mm cartridges there are. Different bullets, different nomenclature, etc. There's a ton of variety in how you make a bullet, even beyond "broad" varieties like hollow point vs jacketed vs semi-jacketed vs wadcutter vs semi-wadcutter... or the actual metal composition of the bullet, jacket, etc. Different rounds are also loaded differently, you can have some under-pressured for subsonic if you're running suppressed, there's usually some variation in what's "standard" and bodies like SAAMI and CIP are voluntary and typically define max pressure only. Plus there are overpressure (+p) and over-overpressure (+p+) rounds... Lots of complexity from over 100 years of a lot of people developing their own ideas than merging them only sort of. |