From a gun “horsepower” standpoint, one 20 mm cannon is equivalent to three .50-caliber machine guns. The 20 will go through .75 inch of armor at 500 yards, while the .50 cal will go through only .43. Also noted that the cannon barrel is not as susceptible to being damaged with long bursts like the machine gun’s.
There are disadvantages, of course, the time of flight of the 20 mm shell is longer, .75 second for 500 yards as compared to .62 second for a .50 caliber bullet. The 20 mm installation is also heavier, one half as much ammunition for the same weight. The 20 is lethal enough to get far more results out of that 200 rounds than the .50 ever will get out of the 400 rounds.