Having spent some of my formative years making pistol bullets on a lathe when the boss wasn’t watching I can say that to turn the subtle blended radii on a bullet is not an easy task. Curves are the hardest, blending two radii into a flowing line is next best thing to impossible unless you are really good or you have some really good equipment.
It would be easier on a computer controlled lathe but then you have to program it and that would be a task by itself.
I don’t know what it is but I would say it is a proper job and not somebody’s lunchtime project for a keyring or pendant… Apart from anything else the remnants of lacquer give it away as something Kosher.
Note also that the turning marks on the bullet are evenly spaced which means it was done all in one go under a power feed. If it was done by hand they would speed up, slow down and overlap. I would say it was turned against a template or witness plate in an industrial process.
Maybe some sort of a go/no go gauge, but in aluminium? I don’t think so. Could it be a starter round for a M/G belt?
Falcon is our lathe man, what does he think.