I have to say one thing about the .50's.  I am an Army Combat vet and Ive seen the "Ma Deuce" tear through almost anything including armor.  I will back P1 up on this, the .50's should take any flimsy airframe to piece's in the WW2 era.  I have the same problem, I can lace an nme ac with .50's and he continues flying, but then I can do the same with another type of MG and destroy them almost instantly.  Now, I am just wondering what a good convergence for the 190 series 20mm cannon ballistic wise, and also the Hispano's on the Spit's and Hurries