OK, hopefully someone has some information on this cartridge. It is a steel cased US Navy 3 inch/50. The puzzle is that it is an APFSDS loading. A friend of mine at one of the Naval proving grounds said he could find no record of an APFSDS loading in 3inch/50. On the overall view you can see four screw heads flush with the case surface. There are four more 180 degrees out on the other side of the case. These hold two rails inside the case for the fins to ride on for stabilization. The penetrator is 40mm in diameter and 275mm long forward from the 4-piece steel sabot. Anyone know of this round or have a similar one? There is no headstamp or any other markings on any of the components.