.50 BMG (.50 Browning Machine Gun), also known as 12.7×99mm NATO, and designated as the 50 Browning by the C.I.P., is a .50 in (12.7 mm) caliber cartridge
British .303 inch (7.7 mm) round and named "Browning .303 Mk II" in British Service. It was essentially the 1930 Pattern belt-fed Colt–Browning machine gun