two shots rang out in reply ; the first missing the guy on the left flank , the round travelling straight through the breeze block construction of the lockup ; the only clue to its power being a puff of dust ebbing away from a small hole in the wall ; but the second shot , fired at the man running for the right flank , entered the mans skull at 950 metres per second and exited his skull a millisecond later taking a 2 inch piece of skull and scalp with it .