303 Enfield first refered to the converted Martini's and then to the very first Enfield Bolt guns, as they where made at the Enfield armory,, then during WW-1 with the advent of the 1917 Enfield it confused the issue a little ,, as the Americans used it in 30-06 and the Britt's in 303 British,, so most Americans just short'en it to 303 Britt, and most ammo compianes in later years followed