As far as I know, the "effective" range (well, the range you can HIT with the cannon) is about 200 yards. I know that is about the range of the 30mm cannons that the LW planes have. The rockets I've never been any good with, but I usually wait until I'm d500 or so before firing, and I always fire 2. I've heard they are accurate out to 1k if you make the approach in a 45degree dive.