“...Interesting to know about the 8mm. Were they ammunition left over from WWI?” kiryandil, post 59]
303 British (7.7x56Rmm) and 8mm Mauser (7.92x57mm) were both adopted in 1888, for the Lee rifle and the Modell 1888 Kommissionsgewehr (Commission Rifle) of Britain and Imperial Germany, respectively.
The Brits used various modifications of the Lee system chambering 303 until 1957. The Germans adopted the Mauser system in 1898 and used modifications chambering 7.92x57mm until 1945. Both nations used various models of machine gun in their respective rifle chamberings during the same periods.
303 British held out for a longtime.