Is it like that story about Blackhawk Down, where soldiers complained that rifles with lower calibers were more accurate but had less stopping power?
Hyper-quick history of rifle calibers for military use:
- late 19th century you get smokeless powder an' shit, everyone uses fuckhuge "full-power cartridges" like 7,92x57 Mauser or 7,62x54R on long-as-fuck-rifles
- WW1 everyone keeps using fuckhuge full power
- WW2 happens, Germans develop and deploy the first "Intermediate Cartridge" , 7,92x33 Kurtz, for the STG series of rifles, realizing that most combat is done on a range of about 300 meters and that with a smaller cartridge you can carry more ammo, control properly full auto in close combat and that you don't need a rifle that can shoot 1km away because no grunt is going to hit anything at that range
- Soviets get 7,92x33 Kurz captures in 42, they develop 7,62x39 (AK ammunition) for the same reasons
- Americans post WW2 are retarded and force all NATO to get a common full-power cartridge, 7,62x51, because they're retarded and no one can say no to the US
- Oh shit 7,62x51 isn't good for grunts, in the 60ies the Americans get out 5,56 (I know, .223 really but DETAILS) because at combat ranges they work the same, you can carry more ammo, control properly full auto in close combat and that you don't need a rifle that can shoot 1km away because no grunt is going to hit anything at that range
- Soviets get 5,56 and they develop 5,45x39 for the same reasons
- Cold War ends, nothing happens
- Memes today for 6,8mm polymeric ammo
Stopping power is kind of... memetic. For combat purposes at reasonable range with no optics (the vast majority of WW2 - Cold War combat) you have no chance to hit anything at 400+ meters and a full power cartridge is essentially only useless weight and can't control them in full auto
properly. You use full-size stuff just for marksmen an' shit.