Neuton's ballistics, especially considering the powders then available were a bit inflated, I think. Even IMR4350 was in the future, I believe.

Newton's case was pretty close to an 8x68S case, necked for .358" bullets - just thinking aloud - seems to me I looked those measurements up once, same base at .522".

The .358 will drive 250gr. about as fast as needed for any game in Normth America and lots faster than any of the mediums used in Africa. A premium bullet should be used due to it's speeds, however for pure accuracy, mine liked 62gr of IMR3031 with a 250 Speer. I once beat a 6x47 BR rifle, group for group at 100 yards using that load. My largest 5 shot group was well under 3/8". That was a factory BRNO rifle. This round will shoot if you've the tenacity to extract that accuracy from something that kicks about the same as the .375H&H - mine did, but not quite that hard with that load. I think it will easily do about 2,850fps with 250's, but I'd prefer a 280gr. to 300gr. if possible. I suspect Woodleigh or Barnes has a good bullet in .358".