On for the ex forces amongst us, or others with knowledge of firearms perhaps. I picked up these 2 items a few years ago during a tramp across the top of a range used by UK Armoured Regiments. The top item is clearly a copper jacketed, iron cored .50 calibre round, the bottom one has me baffled. Its diameter across the impingement rings is around 10.8mm and it seems to be solid carbon steel. The .50 cal has clear rifling marks, the steel one none, maybe the steel doesn't get marked up like a copper jacket or it was fired by something smooth bore. What fires rounds like this?