Even before the war the Germans (and others for that matter) had figured out that 7.92 ammo was far too weak to be a reliable damage dealer against aircraft. You either needed a larger caliber or a large amount of machine guns. Most nations went with the bigger caliber (.50 or 20mm). The British notably kept using their .303 MG on Hurricanes and Spitfires, but used a lot of them. In the case of the Hurricane up to 12.