Found this link on the forums explaining and comparing the differences between ammo, gun effectiveness and firepower by plane type.  I think it’s very well organized and informative page worth a read.

I know someone posted something like this before but I couldn’t find it.  


http://www.quarry.nildram.co.uk/WW2guneffect.htm

My Favorite part is that the outstanding performer is clearly the German 30 mm MK 108, which achieves ten times the destructiveness of the .50 M2 for only twice the weight. It makes a particularly interesting comparison with the MK 103, which fired the same M-Geschoss projectiles. The MK 103 gains an advantage because of its higher velocity, but loses most of it due to its lower rate of fire, then is finally eclipsed in efficiency because of its much greater weight. No surprise that the Luftwaffe considered the MK 108 their premier air-fighting gun despite its low muzzle velocity. The Me 262 jet fighter, with four of these guns clustered in the nose, completely outclassed the firepower of every other WW2 fighter.S~TX-FlightRisk Green 3

Yep the Germans clearly dominate the firepower categories.  What I thought was interesting is that although the 108 was ten times the firepower of the .50 M2 by using six to eight guns the firepower ratio for German to US drops to 2 to 1 or 3 to 1, depending on plane types used.  Not to bad I guess but still and overwhelming edge the German planes.  Another thing is after all I have heard about how good the Russian guns are for the most part they didn’t rate high as I was lead to believe – plane firepower and ammo firepower.   Interesting.