The modern bullet is based on a version invented in 1826 by Henri-Gustave Delvigne, a French infantry officer. Delvigne's bullet had a spherical shape and was rammed into a breech's rifling grooves.
According to Princeton University, the word "bullet" is translated from the French "boulette," which means little ball. "Boulette" describes the original musket bullet, which consisted of a small lead ball wrapped in a paper cartridge that held the bullet in front of explosive powder. The muzzle-loading guns that followed had barrels with the rifling grooves Delvigne's bullet used. The grooves required ammunition with a tighter fit than early lead balls provided.
Delvigne's bullet fell out of favor because it was difficult to aim, and it failed to hold its shape when the rifle was fired.