Federal Premium Vital-Shock Rifled Slugs were designed for maximum performance and reliability. Federal realized that the majority of slug hunters use a traditional smoothbore rifled slug ammunition and they set a goal to make a smoothbore slug that was more effective and accurate than traditional designs. What did Federal do to make a more accurate slug for smoothbore slug hunters? They came up with the TruBall Rifle Slug. This is a slug that uses a simple plastic ball between the wad and the base of the slug. When the round is fired the ball centers the slug in the barrel. This self-centering design makes this slug extremely accurate. Upgrade your smoothbore without changing barrels.