Perhaps a roller mill that jewelers and metalworkers use to thin metal. https://www.amazon.com/Rolling-Mill-Jewelers-Grade-Rollers/dp/B000RB5CXC
Yes... I was a horrible abuser of pocket change as a lad. I placed many a cent on rail tracks, spooned lots of nickels..... It’s just the sort of thing youngsters did before we had video games and smart gadgets in our hands.
Only once did I put a cent on the rail tracks. Not sure what became of it. I was too into spending my change, myself stay on candy. Way back then a Cent wound buy a few mouthfuls.
When I was a child my friends and I would put pennies on the LIRR tracks. After the train ran them over there was nothing readable on them. Just a piece of flat elongated copper.
It is copper and it weighs in at 3.g. My best estimation is a Lincoln Cent. The tracks (spur) where it was located have been out of service for more than 40 years.
Maybe it was a Wheatie. Not that that makes any difference, but I always liked to scry out the faintest details on my mystery metal detector finds. Found a rough slug of a copper in an old colonial (Rev War era) sand road bed, once. Almost zero detail left on it, but from the diameter and the faintest ghost of a portrait on it (which was only visible at certain angles to the light), I surmised that it was a French copper of Louis XV. Love those little puzzling mysteries, sometimes.
I have witnessed this many times as youngsters will place coins on track and watch them as they hard to find sometimes when they fall off rail into ballast ,,you have to dig a little sometimes. There always a few places that people will park and walk down to smash coins. they sometimes stack them on top of each other and smash them together or try to.... vibration sometimes they slide off rail