I flew across town to trade brass with a fellow shooter. He had some .223 and needed 9MM Luger. I'm in the opposite condition - fat on 9MM and thin on .223. In reality I could have bought the brass for less than the cost of the gas for the trip - but making the trip was a reward in itself.
Turns out he is a postal worker. With an MP5. And now a suppressor. He needed the brass to load some subsonic rounds.
(Insert your own "going postal" joke here).