As far as I recall the 50cal jam rate was very low on M2s. The "souped up" M3 had problems with the metal parts actually cracking from the increased force. They weren't designed to do what they did.
Guns that are actually designed to do certain tasks usually don't jam as much.
That's why I hate how in TW any plane you fire that has any gun for more than 5 seconds will jam the gun. No matter how historically reliable it was, or despite the fact that many had recocking/clearing levers in the cockpit (and the guns are in there too!)