Crazyguy,
I thought a AK was a 308 caliber or equivalent?
An AK 47 fires a 7.62 X 39 bullet. A .308 rifle like the HK and others fires a 7.62 X 51 bullet (Informally known at one time as .308 NATO.). The latter cartridge is much more powerful than the AK 47's cartridge.
In the image below the middle two cartridges are the 7.62 X 51 side by side with the 7.62 X 39 (Russian).