Originally Posted by sputnik1988
Actually the SKS was designed and saw trials during WWII, the AK was designed later, they are totally different and neither is based on the other. The 7.62x39 was based on the 7.92x33 kurtz as a lighter recoiling 7.62x54R, more suitable for battle. the 5.45x39 was designed after the 5.56x45.
You are correct about the accuracy vs penetration though.
5.45x39 is cheaper, recoils less, is more accurate and is more suitable as a 'combat' round.
7.62x39 is better for hunting (with proper ammo)
He is only partiality correct, if you get the right ammo it will penetrate.
Check out the link below where it says Enhanced penetration cartridges.
The original 5N7 standard service cartridge didn't have much penetration but the 7N6 that is what most the surplus ammo out today, does penetrate quite well. I have shot it through 1/2" steel at 100yds.