By filling the open space behind a pre-scored, full-metal case with a polymer ball, Federal has created one of the most reliably feeding and expanding bullets available. By making these bullets in lightweight offerings, it has also created low-recoiling ammunition. The 105-grain 9 mm load is just one example. Penetration is, in my mind, an optimal 9.5 inches. That, combined with the high velocity and wide expansion, helps to create a wide wound cavity for this light-recoiling 9 mm personal-defense option.