The one I played with for a while was regulated for the 300-grain bullet over 42gr cordite. Had an option to buy, but passed it up: bores were stuffed and it wouldn't shoot. I will look up the load I used, probably ADI powder, but it won't help you much for the 250-grainer.

Its a pity Graeme Wright is silent on this cartridge, he even recommends a modern load for the .369 Purdey (!) but misses the .333 altogether.