I have a .300 Martin Engfield jsut converted (because of the rotten bore) to a .375 express 2 1/4. Ok, not quite the .375 2 1/2" flanged of famed past, but, a .303 Brit. rebored, necked up and reamed for .375 bullets. I am working loads now that I have 20-30 cased necked out. I gues I can develop loads close to a .375 win to lower limits of .375 JDJ. I'll let you know.