I heard a great story from a friend who had been talking to some Czech Squadron air aces that fought in the Battle Of Britain.
The 303 calibre Browning guns (there were 8 on the Spit) were set to converge at 400 yards .. the Czechs .. in general more experienced and older than the young Brits had the technicians re jig them so that they converged at 100yds so that could get up close to the Luftwaffe planes!