I've fired irl both a 5.45 and 7.62x39 AK, you are correct more or less, they wanted the advantages of a 5.56 ish caliber, without needing to change training doctrines. Good video, and early happy Thanksgiving Sir Snipothy
PROTIP: The 545 has a trick to it; it has tiny vertical kick for the first 8 rounds before its recoil veers sharply to the right. The correct play is to do short, controlled bursts with it and it becomes a laser gun. I run reduced capacity mags on it because I stop firing after 10 rounds regardless, so 2 salvos of 10 makes for a super mobile and accurate weapon.
I read somewhere years ago that the Soviet Union took experience from its AKMs being used in Vietnam and its competitor the M16 that the 7.62 is a bit more powerful but US soldiers could carry more ammo since the 5.56 is lighter and more controllable
ah yes the beacon of light, Sick Snipes himself again with his first Call of Duty experience shedding his absolute superior firearms history and prowess unto mere mortals like us.
Considering the ranges at which most MW2 gunfights happen, I think the 5.45 should be the one with the 3-shot-kill potential and the 7.62 should be 4, but with better penetration. 5.45 is notorious for yawing and tumbling and causing extremely grievous wounds, 7.62x39 has a tendency to pencil-poke unless it hits bone.