Wesley Richards Explora (12ga) and Fauneta (20ga) cartridges. These were for ball-and-shot aka paradox guns. The projectile is actually a lightweight hollowpoint slug, the cone you see sticking out the shell is a hollow sheetmetal aerodynamic cap.

This might be on the edge of the definition of "rifle cart" since these were for ball-and-shot guns--basically shotguns with rifled chokes, but I always thought the Westley Richards Explora and Fauneta were cool. The projectiles are actually fairly light slugs with big hollow points, the cones you can see sicking out front are very thin sheetmetal aerodynamic caps.