This muzzleloader version of the X-Bullet is 100% copper with a large hollow cavity for quick sure expansion. Barnes Expander MZ Muzzleloader Bullets produce more consistent shot-to-shot velocities and better accuracy for greater shooter confidence and more one-shot kills. Expander MZ bullets deliver deadly performance at both high and low velocities. These tough deep-driving bullets typically retain 100% of their original weight. They expand to twice their original diameter creating six razor-sharp copper petals that slice through game.