You cited a document from the end of the war, Feb 1945, the war started in 1939 so what do they do in the 5 year gap?, you also stated an opinion from Harris that .50's should be fitted which is then refuted by your own evidence that it would cause CoG problems, the British never got the .50 until the lend lease agreement was activated in mid 1941 long after the war had started and planes had been designed, you also haven't explained how your going to fix the sighting issue for the years 1939-44 after you remove tracer rounds. Let's be clear I'm not saying the .303 is better than the .50, what I'm saying is you need to take into account the timeline of when different weapons could have been issued and the issues involved, the .50 was not a reliable air weapon until mid war, both the guns themselves and it's ammunition.