Angle of attack, figure (top view) /// \\\ Hitting a flat surface vs. ||
The more square the round is hitting the object the better, the difference between a deep penetrating .50 cal vs. a grazing or ricochet. Difference between hitting a man square in his jaw, vs. glancing off his jaw bone.
And if you think this untrue, please take up a p40B (or any cannon/mg nose mounted A/C) vs. any x4 .50 cal winged A/C, fire only the x2 guns on that a/c for few flights.
That is why i ditch the .50's on the p39Q, the guns poor angle of attack make them almost not worth having (in a game) where in reality anything that hits, is better than not.