The Charlton Automatic Rifle was to act as a substitute for what First World War-era light machine gun of US design?
Lewis gun The Lewis gun (or Lewis automatic machine gun or Lewis automatic rifle) is a First World War-era light machine gun of US design that was perfected and mass-produced in the United Kingdom, and widely used by British and British Empire troops during the war. With its distinctive barrel cooling shroud and top-mounted pan magazine, the Lewis served to the end of the Korean War. It was also widely used as an aircraft machine gun, almost always with the cooling shroud removed, during both world wars.
.30-40 Krag The .30-40 Krag (also called .30 U.S., or .30 Army) was a cartridge developed in the early 1890s to provide the U.S. armed forces with a smokeless powder cartridge suited for use with modern small-bore repeating rifles to be selected in the 1892 small arm trials. Since the cartridge it was replacing was the .45-70 Government, the round was considered "small-bore" at the time. The design selected was ultimately the Krag–Jørgensen, formally adopted as the M1892 Springfield. It was also used in M1893 and later Gatling guns.