Vince, I appreciate your fervour, and once again I didn't call them crap, all I did was looking at facts, not pilot reports (which can be fallacious) or Wikipedia, and my comments are based on my studies on the real ammunition that I have together with the data that you provided.
I also had the luck to see a Breda Safat and an M2 for real: I got the chance to study them deeply, and again there are many things that could have been done in a better way. The fact that we didn't use them after the war, and that the M2 is still rocking around, should say it all on which one is the best anyway.
As for the B.17 being shot down: it really is remarkable, but it's a rare if not unique case I believe. When talking about shooting down a plane there are many factors that need to be taken into account; anyway, once singled out of a formation it would have been an easier target to knock down, since all you need to do was hose the cockpit area with your weapons, and that can be done effectively with any machinegun.
Once again Vince, I'm not saying the Breda was crap, I am saying that it performed poorly compared to what the Germans and the Allies had available for the same caliber, besides the number of guns was not sufficient to give a strong punch. Up close they would have been effective as any other heavy machine gun, but from a distance you couldn't achieve the effective and deflected shots which were typical of the US .50cal
Imagine having to approach a plane that is shooting back at you with a more effective weapon and you have to get well within its firing range to place some effective shots..
Or as a friend of mine says: imagine having to fight against a guy with a whip and all you have is your trousers belt.. You'll be able to hit him, but you'll have to get really close, and the pain he'll cause you will be much more than what you can cause him
That is the reason why (no, not the belt/whip thing!) the Germans developed the Mk.108: they needed to deliver a tremendous punch in the smallest time available and without taking too much care for accuracy. We had to aim for the cockpits, the Germans hosed the B-17s and B-24s with explosive bullets the size of a fist, literally tearing the planes down!!