In the Army you have to return 90% of the brass, by weight, that you sign out.
There was a time back before 1968 when anyone who wanted the brass was allowed to keep it. All other brass was turned in. I got many a case for reloading from the Master-at-arms when I was given handgun training at the Airbase.
Then Bobby Kennedy got shot and hysteria gripped the USA. From that time on the Sargent in charge was not allowed to give out free brass and all that was used at the interior range had to be accounted for.
So I started scrounging at the local military rifle range. Most of that had to be turned in, but I still found lots of 5.56MM and .30 M1 carbine brass.