Cylindro-conoidal bullet

The cylindro-conoidal bullet was invented by Captain John Norton of the British 34th Regiment in 1832. It had a hollow base, so that, when fired, the bullet would expand and seal the bore. The origin of his idea is an interesting one: when in southern India, he examined the blow pipe arrows used by the natives and found that their base was formed of elastic locus pith, which by its expansion against the inner surface of the blow pipe prevented the escape of air past it.[1]

Two Civil War cylindro-conoidal bullets

In 1836, Mr. W. Greener, a London gunsmith, improved on Norton's bullet by inserting a conoidal wooden plug into its base. Although both inventions were rejected by the British Ordnance Department, the idea was taken up in France, and in 1849 Claude-Étienne Minié adopted Greener's design and produced the "Minié ball".