Good shooting skills at 8000m!

I personally shoot at less than 1000m and usually as coup de grace in early war, you know, their rapid firing cannons in later war kills.
I havn't tried shooting for a long time. My last time is outfitting a Type VII as a U-Flak and downed more than 20 enemy planes. Though the boat get pretty ruined aftermath. But that is on vanilla SH3. Dare not try it in GWX after a failure to sink a great merchant (found it has 2 or 3 cannons, many flaks, so on)
Now playing NYGM using Type XXIII... Grr. no flak nor desk gun = no shooting. Anyway, in later war, shooting is suicidial, especially at British coast