I think he is asking for someone to load ammunition. I would ask gunsmiths in your area. Seems it would be more sensible to sell the 358 Norma and but a .375 with loaded ammunition available. Just a thought.Dear Mike,
"IF" the case you want to load is the 358 Norma necked up to .375 it is the same as the 375 Chatfield Taylor I have used for years. Loads for that are below.
65.0-72.0 Grs Benchmark for about 2900 fps with the 270 Hornady bullet.
67.0-72.0 IMR 4350 for about 2700 but the case is 100% full.
If it is the 358 Norma using a .358 diameter 375 gr bullet[ didn`t thing they went that heavy] then you are out of luck because I have never done anything with the 358 Norma.
P.S.!!! Loads are safe in MY rifle! They may well be too hot, in yours so stat low and work up looking for the normal signs of pressure.