The Volcanic ball, officially known as the No.1 and No.2 pistol cartridge, was the first true self-contained unitary firearrm round, and a key step in the development of the metallic cartridge.
The Volcanic Ball was a development of Walter Hunt's Rocket ball design, itself based on the earlier Minié ball. The Rocket Ball incorporated a charge of powder in the base of each round, but was of a caplock ignition type: the Volcanic Ball added a percussion primer to the seal at the base of the bullet, creating a complete round.
The round represented a significant improvement over paper cartridges in that it was durable enough to withstand the rigors of mechanical loading, and the Volcanic Repeater series capitalized on this with their lever-action mechanisms and use of tube magazines containing up to 30 rounds.
While revolutionary in historic terms, the Volcanic weapons were not a commercial success: the rounds were severely underpowered and the pistol variants of the Volcanic Repeater were very large and bulky compared to period revolvers, and difficult to operate without using both hands.
A Volcanic Ball consists of a standard Minié-style bullet with a hollowed-out base: into this base is sealed a powder charge, with a base of waxed paper with an added brass ring on later models. In the middle of this a percussion primer is added.
It is debated as to whether the Volcanic Ball represents an early example of caseless ammunition: while there is no actual case, it could be argued that in the instance of the Volcanic Ball the case is incorporated into the projectile.
Due to the very small amount of powder that could fit in the hollow base of the bullet, performance was very mediocre: muzzle energy was in the region of 56 foot-pounds, less than a modern .25 ACP round.