Tim,
After studying your dimensions, I believe the most likely cartridge is the 11.15x65R LK express, considering that the chamber will be larger than the cartridge, and that the LK express was very popular. Two other possibilities are 11x65 Collath and 11.15 Stahl Express. While both these have a bullet diameter slightly larger than the dimension given for the "slug", it seems that both were available with the Tesco express style bullet. This is the style bullet used in 9.3x72R and 8,15x46R ammo because it can be used in barrels of varying diameters without unduly raising pressure.
Mike
