Its .577 tyranosaur. It is one of the most powerful cartridges available for bolt action rifles. It was designed to stop a charging elephant dead at around 10 yards, the maximium distance a PH is allowed to shoot one at if their client wings it. It has almost 11000lb muzzle energy thats about 5 times the energy of a .243. A serious round for some pretty dangerous game. It would be fun to have a go though wouldnt it.