I have been doing some reading on the 358 WSM, otherwise know in Australia as the 35 Sambar. Cartridges of the World 11th Edition by Frank C. Barnes has it listed as a Wildcat Cartridge developed by Breil Jackson. The article on page 214 states that the 35 Sambar is a 300 WSM necked up with no other changes. The article also stated that 2700 fps can be achieved with 250 grain Speer GS bullets from a 23" barrel. For comparison the 35 Whelen ranged from 2400 fps - 2500 fps with various 250 grain loads and the 358 Norma Magnum ranged from 2500 - 2800 fps with various 250 grain loads. Just from the velocity comparison the 358 WSM should be a decent enough cartridge, even for hunting big game here in Alaska.
Anyone ever think about having one built or own one already? If you do I am sure forum members would really like to hear about it. Thanks