Underwood Ammo 817: The Xtreme Defender is based on the popular Xtreme Penetrator product line. The XD ammunition has an optimized nose flute, total weight, and velocity to achieve a penetration depth up to 18 inches with a permanent wound cavity (PWC) that is just simply enormous. Not only is the PWC over 100% larger than any other expanding bullet, expansion is achieved despite being shot through barriers.