Short answers, pulled from the story.
Claude-Étienne Minié unveiled his hollow-based bullet design in 1849. James H. Burton later improved upon this initial concept at the Harpers Ferry Armory by adding a deep conical cavity to the base of the projectile.
The projectile took on a cylindro-conoidal shape with a cone-shaped hollow at its base. The resulting bullet weighed 1.14 ounces and traveled faster than previous versions while offering better range and energy.
The Minié ball solved loading difficulties by allowing a loose fit that slid easily into the gun before firing. When fired, the lead skirt expanded under pressure from deflagration to grip the rifling grooves effectively and create a tight seal between the bullet and the bore.
The Minié ball came to prominence during the Crimean War following its initial development. It then became standard issue during the American Civil War where it was used in weapons such as the Springfield Model 1861 and the Pattern 1853 Enfield.
Conical projectiles possessed higher muzzle velocity and greater mass than round balls which often lodged inside flesh. If the projectile struck bone it would shatter that structure completely causing severe compound fractures requiring immediate medical attention.