why are so many firearms in WWII 7.62mm? (Or pretty close)

Question

I’m not ignorant of firearms at all, but it strikes me as odd that in the 20th century, most firearms ended up using cartridges that are all more or less similar sized .30 caliber bullets, even pistols, although they tended be less powerful bullets due to smaller casings and less powder

In: 6

Answer 1

Just to name a couple or few reasons…

Ballistics are very good for the 7.62/.30-cal’s with holding accuracy, trajectory, and lethality at ranges that were common in WW1, WW2, and Korea. The 7.92/8mm & .303/7.7-cals were very close.

Anything larger was usually of more recoil with less accuracy down range. Anything smaller, (6.5’s say), were less lethal at longer ranges.

Edit: Should note, for those unaware, this is for rifles and smaller machine guns.