I have rebored a .303 MH to .375 and use necked up .303 cases. I have the rifle ready to start the tests, but have yet to load and shoot any cartridges. I intend to shoot 250-270 0r 300 gr cast bullets. I will also try some jacketed bullets. I expect I should be able to push the 250 grains to 2000 fps.
I will post my results when I can accomplish this.