What is the most powerfull assault rifle?

Answer 1

There are many powerful assault rifles. The highest caliber assault rifles currently would use 7.62x51mm, or .308 caliber. Guns such as The FN FAL, or the H&K G3. You can't really narrow it down effectively because with the right equipment, you can make a gun any caliber you want. The problem lies in the practicality. A 20mm machine gun would destroy anything it came into contact with, but it would break the shoulder of whoever was firing it. A .22 caliber machine gun could fire at an incredible rate with little recoil, but wouldn't be very effective unless you pump a lot rounds into the same place. In terms of practicality, a 7.62x39mm Assault Rifle (like an AK-47) would be more powerful than an assortment of rounds, and is somewhat controllable compared to larger caliber weapons.

^^^ Wrong. Any rifle that fires a .308 is considered a battle rifle, not an assault rifle. And the 7.62x39mm is a terrible round. Its powder to weight ratio is very low, it's big, but it's also slow. 5.56 and 5.45 are completely superior.