Get a copy of Pierre van der Walt’s book: African Dangerous Game Cartridges. There is a good bit of information on the 450 Rigby in the book, as well as info on firearms, cartridges, and bullet selection for dangerous game rifles. There is reloading information for the 450 Rigby in the book. Making your own loads will open up a much wider variety of bullet weights and types over what is offered in factory loaded ammunition. There is not any official published load information for the 450 Rigby available from the major manufacturers ( Barnes, Hodgdon, Swift, etc). However, you can REDUCE the load info for the 460 Weatherby Magnum by 5%, and if I remember correctly you can reduce load data for the 450 Dakota by 2.5% for use in the Rigby. Good luck with the rifle!