try this and you cant miss
P47 with 8 50cals
set inside pair 300 next pair 325 then next 350 and finally 375.
this produces a box of fire and its fantastic for ground attack
also try setting 1st 300 2nd 300 3rd 350 4th 350 for devastating anti aircraft shots
I also like 400 as this is the average distance i seem to see when i manage to get target in sights.
cannons should always be set further out than mgs if you are the type of flyer who fires all guns together.if you are finding it hard to hit anything try setting guns like this
1st 250 2nd 300 3rd 350 4th 400....if you miss with this you'd be better off joining the navy hehe