Prior to 2004, production was estimated to be 2 to 2.5 billion rounds per year
. (Layne Simpson used an old reference.)
I can't find a newer reference; but I'm sure we're exceeding that now, especially with the increase in popularity of low-grade trash we like to call "bulk packs".
You mention the depression.....
My father was born in 1918 and thus experienced the depression. His family was poor. He had no father. At an early age he was tasked to hunt for the family (his mother and younger sister). He used to tell me that his mother would give him the single shot .22 rifle and two or three 22 rounds. He was expected to return with a rabbit for each round she handed out to him. No shooting cans for fun for that kid. Tough life.
When I was a kid, I couldn't understand why my grandfather was so stingy. He'd give each grand kid no more than one box (50 rounds) for an entire day of shooting. But, before we could "sling lead", we had to stack up 5-10 rocks and pick them off one at a time as a demonstration of "one shot, one kill".
When we ran out of grandpa's ammo, we'd turn to our dad. He handed it out by the brick (500 rounds), and it was nothing for the group of five to six people to go through 3,000-4,000 rounds in a 6 hour shooting trip.