Is the diameter smaller than normal? Is it wider than normal? Is the outside rim kind of rounded rather than perfectly flat? It could be a slot machine coin. I've seen coins that were pulled from service because they got stuck in the slot machines. They were mostly 'silver dollars.' They were reduced in diameter and the rim was wider, caused by the constant pounding the coins endure.
Collecting nut. Please explain to me how a worn die can cause different effects across the edge of a single coin?