Yea, what Eagler said, Also, What i do with cannon is set conv to 400 and for trailing shots, aim a little high, like as high as the enemy aircraft's vertical stab, typically with success.
For deflection shots,,,,,they are a bit harder to judge, practice, practice, but my thoughts are that the nik's cannons are wicked effective and its not a bad turner either. a tad slow tho