Made from an actual once fired .303 cartridge.

.303 British, or 7.7x56mmR, is a .303-inch (7.7 mm) calibre rifle and machine gun cartridge first developed in Britain as a blackpowder round put into service in December 1888 for the Lee-Metford rifle, later adapted to use smokeless powders. It was the standard British and Commonwealth military cartridge from 1889 until the 1950s when it was replaced by the 7.62x51mm NATO.
The .303 cartridge has seen much sporting use with surplus military rifles, especially in Australia, Canada, New Zealand and to a lesser extent, in the United States and South Africa. In Canada, it was found to be adequate for any game except the great bears.