Check out this awesome video on the most powerful AR-15, called the Falkor Petra 300 Winchester Magnum.
Compared to the other AR-15 shown, this thing is enormous. It shoots a bullet roughly twice the size of bullets shot from his other Ar-15’s. It even weighs 4 times the amount as the other one. The AR-15 weighs only roughly 10 pounds since it has a carbon fiber barrel.
This gun has pinpoint accuracy and is incredibly powerful. Check it out!