Guy brought in a "20 gauge" Browning Shotgun that had a shell trapped between the closed bolt and the lifter: got it cleared and he want it test fired to make sure it was operational....loaded a couple shells, popped one and I knew something wasn't right: got it cleared and the hull was blown out at the base.... wasn't a 20 gauge at all but a 16 gauge.
More than once I've run into guns stated as being one caliber only to find they weren't.
.270 Winchester when the rifle was actually .280 Remington
300 Win. Mag. when it was .300 Weatherby.
Lesson: READ the fucking writing on the barrel FIRST, never mind what the Customer says!