I am no expert on firearms but i know that a 9mm bullet is bigger than a 6.5mm or a 7.62mm (obviously) i am also aware that a pistol's bullet has a very different aerodynamic shape to rifle bullets and at 5 meters the pistol bullet will cause the most damage because of its lower muzzle velocity and its larger size/flatter shape however the pistol bullet will lack in penetrating power so i can understand if it fails to penetrate armor.