I thought .50 caliber armor piercing incendiary were badazz. My commander had fun with those. Brought down a large tree. 
We lost a lot of Marine fighter planes to Japanese Zeroes.
Marines had .50 machine guns on their fighters.
Japanese had .20mm cannon.
.... The Marines were getting shot down before they could get in range with their .50's.
There is a big difference between .50 cal and 20 and 25mm.