Does anyone know a good source of load data for obsolete British sporting cartridges?

I've recently purchased an old Westley Richards cape gun chambered for 28 ga. and .300 Sherwood and can't find any specifics on the .300 Sherwood loads.

Bertram still makes brass, but I haven't any idea where to start with regard to bullet type or weight nor powder types or charges.

Any info anyone can offer would be a great help.

Spinfantry