I knew an old man who was a teenager in the depression. He told me that things were pretty bad here in Arkansas then. People were poor before, but they were starving in the depression. They couldn't afford shot, or powder, or primers in that house, so he hunted with a bean flip (forked twig with latex strips and a leather pouch). He said he used 3/8" steel knockout slugs to kill rabbits, but he had a few 1/2" steel ball bearings he would use to kill deer with. He said the trick was to get real close and hit them within an inch of the sweet spot in the head.
That's rough livin right there fellers! So I laugh a little when I hear folks talking about what they think is minimum for shooting deer with.
Anything is better than a steel ball bearing going 300 fps!