A muzzle loading firearm projectile is disclosed that is composed of a
multi diameter, hollow base solid copper bullet, the rear cavity filled
with a material of low-density, and a gas pressure seal that separates
the bullet from the powder charge. The majority of the bullet shank has a
diameter less than the bore diameter of the firearm barrel to allow for
ease of loading and alignment of the barrel and bullet axis; a narrow
ring of material larger than the barrel bore diameter but less than the
groove diameter is located at the junction of the bullet shank and nose
profile that centers the bullet in the barrel and positively positions
the bullet over the powder charge regardless of orientation of the
firearm. The low-density material filling the rear cavity of the bullet
acts as an expansion medium when impacted by the rear gas seal during the
firing process causing the hollow shank of the bullet to expand and lock
into the barrel rifling.