Originally Posted by ThaGoat

What he's prob referring to is the UN agreements on calibers. The US army uses the 5.56 and 7.62 rounds. Russia uses the 7.62 and some others. Odd thing is, is that we can't use their 7.62 in our weapons but they can use ours. Wonderful design flaws. I can remember when I was in the service (many many moons ago) and this being explained to us. Saw something interesting the other day. the 5.56 round is really just a beefed up .22cal round. Difference being the size of the casing and slightly longer bullet. Some of you may not realize that the 5.56 and 7.62 rounds are designed to tumble on impact instead of the projectile exploding. Another UN thing I think. The basis is to "wound" and not "kill".
(I may be totally wrong, but I believe its what I remember on the rounds.)

The NATO standard is 7.62mmX51mm. The Russian is 7.62mmX39mm ("7.62 Soviet"). The NATO is basically a .308 Winchester, it's a full sized battle rifle cartridge. The Soviet is comparable to the 5.56X45mm, it is an intermediate assault rifle cartridge. The Russians have the 7.62X54mm ("7.62 Russian") cartridge which despite being over a century old is an excellent round used in,for example, the Dragunov. Originally developed for the Mosin Nagant bolt action, it has not been out of service since it's creation. AKs are chambered in 7.62x39, until they switched to 5.45mmX39mm for the AK-74 and AKS-74U.

When the 5.45 came out a lot of people were worried the Soviets had developed a super wounding bullet that would create large wound cavities by tumbling inside the body. Studies showed the new 5.45 was not producing any kind of super wound effects as compared to the NATO 5.56.