50's work and work well, when in their element.
For one, you need convergence. More guns hitting the same spot results in more broken stuff created.
Two, you need time. While 50's did have API rounds, most of what they spat out was slugs, which dont go boom. So on order to do damage you need to dump lead into a spot until something breaks.
And three, you need to concentrate your fire on a smaller area. In your post, you said that you sprayed a zeke from wing to wing. What you likely did was put a bunch of holes in the skin, but since you did not concentrate your fire, nothing critical was shredded.