As revolutionary as rim-fire cartridges were, they had some disadvantages. The biggest was the cartridge itself, which needed a thinner shell to ensure that it would deform when the hammer struck it. But the thinner casing limited the explosive force it could contain. As a result, rim-fire cartridges held less powder and generated less firepower.
To overcome these limitations, gun manufacturers quickly evolved the cartridge so it could incorporate a percussion cap, filled with shock-sensitive primer, within a unified, thicker-walled structure. The cap sat in the middle of the shell's base, which is how it came to be called a center-fire cartridge. Gunmakers also had to modify their weapons to fire the new cartridge, including either a firing pin or a striker. In the former, a spring-loaded hammer transferred its energy to a blunt-nosed rod, which struck the percussion cap. In the latter, the hammer struck the percussion cap directly. In either case, applying a sharp blow to the cap ignited the primer, which then ignited the powder and fired the bullet.
Because center-fire cartridges generate more power, they can fire larger bullets, which makes them the most common type of ammunition used in firearms today.