It was a recently-fired rimmed cartridge-case.
"Wilmshurst of the Frontier Force" by Percy F. Westerman
Also made to shoot .32 short rim-fire cartridges.
"The Bradys After a Chinese Princess" by Francis Worcester Doughty
The chief faults of the rim-fire cartridges are danger and unreliability caused by the action of heat on the lubricant.
"The Modern American Pistol and Revolver" by A. C. Gould
Rim-fire cartridges cannot be reloaded.
"Pistol and Revolver Shooting" by A. L. A. Himmelwright