De Wilde, or armor piercing?

[reflected]

Another source for the Battle of Britain armament gives four guns with ball, two with AP and two with incendiaries (presumably Mk VI) with four of the last 25 rounds being tracer (presumably Mk IV incendiary/tracer) to tell the pilot he was running out of ammunition. It is not clear why ball was used at all; presumably there was a shortage of the more effective loadings. (By 1942 the standard loading for fixed .303s was half loaded with AP and half with incendiary.)

This part is very interesting. So it was half AP half De Wilde after all, except in the beginning, when there was a shortage and they had to use regular ball ammo too.

Using AP only didn't prove to be more effective than half-half. Now I'll try De Wilde only and see, but I'll probably go back to half DW half AP.