Hi there
With regard to the .0303s and other guns;just a few points.
The .303 round fired in the aircraft used some DeWilde incendiary rounds,which were not used in ground-fired weapons.Some .303 rounds are not interchangeable between firearms,eg; the Lee Enfield used a .303 ball round which could be fired in the Bren but had a lower powder charge than the official Bren round,the Ball Mk VIIZ,which could not physically be loaded into the Enfield rifle,because the cartridge was slightly different. Also, it was a fact that many German bombers limped home,despite having been riddled with .303. The weight of fire is what really matters and the German combination of 7.92 (fired at a faster rate than the British guns) and the 20mm Oerlikon shells was much more effective. Rifle-calibre bullets punch small holes in aircraft and often fail to penetrate even light armour or destroy system piping, structures and engines,whereas it takes very few cannon rounds to wreck an aircraft. Quite why the designers didn't go for the Browning 0.5-inch,even when the Belgians were using them in their Hurricanes,is beyond me. The fact that the Germans had a working cannon arrangement, along with the French, is a black mark against the British designers,for not having such for their pilots. Conversely, all sides were guilty of allowing their bombers to go out against their enemies,with only rifle-calibre guns,often in single mounts particularly the Blenheim, the early Ju88,etc.
regards
TDD