What is the most powerful assault rifle?

Answer 1

There is no "most powerful"... It's all about the terminal ballistics of the round the gun fires, a 5.45 won't be more damaging out of one assault rifle than the other. But the intermediate cartridge that has the most damage potential today would be the 5.56. (First used in the M16) Newer mk318 mod0 5.56 is far less velocity dependent, allowing it to fragment more reliably out of shorter barrels. When hit with the speedy 5.56, it penetrates a few inches, then breaks in half, it will proceed to tumble and fragment, creating far bigger wound cavities than any other intermediate cartridge.