I turned a P-51D into confetti at about 1000 yards with the Mossie's cannons once. He was diving away from me and going nice and straight, so I just put the pip on him and held the trigger down as I pulled up slowly.
I used the same trick to nail a fleeing Fw190D-9 with the 30mm spud gun in the Bf109G-6 (this was prior to the Bf109s being redone) at about 700 yards, same result, dead runner.
In reality Beurling shot down a Bf109F at 800 yards using the Hispano cannons in his Spitfire Mk V, and he said it was a deliberate, aimed shot.
Don't say it "couldn't be done in reality" when it could be.
Also Storch, maybe you can't see anything at a distance of one kilometer, but the vast majority of humans can. If we couldn't see things at that range, and much, much further, WWI and WWII air combat would have been essentially impossible.