AP/I rounds are are a compleatly diferent beast than HE/I rounds, HE/I rounds are more efectave aganst defeating the aircraft as per say defeating the means by which it is able to fly. AP rounds kill engines, men and the such, HE/I rounds set it afire, tear pices off it ect, both are effectave, but for different reasions,The Italians, and the Japanese(and others) had HE/I rounds from the start of the war, The Japanese even adopted an Italian design for one of their own.The Breda 12.7mm is not exactely one of the better MG's of the war, the ammo it fires is howeaver a very effectave type.