"[...] the HP bullet can penetrate an 8mm steel sheet out to about 400m, whereas its predecessor could only manage it at half that distance."
In the 1960s a friend was a member of a UK Army reserve. Every year they had a rifle competition between the various groups. The target was a scoring one - but at the start it was blocked by a large vertical sheet of steel. The first person in each group had to hit the sheet at the very top to tip it over.
One year no one could knock their sheet over. It transpired that it had not been tested with their new 7.62 rifles - which had replaced their previous .303 ones. The bullets were just going through the steel.