".303 British, or 7.7x56mmR, is a .311 inch 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."
- John Ousterhout
- There is no such thing as a "Springfield .303 cartridge". While Springfield did make rifles that fired British .303 cartridges, the cartridge should not be called a "Springfield .303 cartridge". The cartridge was almost universally called "Brit 303", "British 303", "Enfield 303", or just "303". I would expect it to have been most likely fired from an Enfield, either a No. 1 (the famous "Short Magazine Lee Enfield" or SMLE, pronounced "Smelly"), or a No. 4 (WWII-era issue to British commonwealth forces except Australia, who continued to manufacture their own SMLE's). The extractor marks on the cartridge might offer a clear indication of the firearm that fired it, and the headstamp would identify who made it and when.