Can't help you with direct loads for the 375H&H but I do load cast in my 404 Jeffery using AR2209 with good results. Obviously the 404 is a little different from the 375H&H but the maximum recommended load of AR2209 for a jacketed bullet in the 404 is 80.0grs and I'm using 63.0grs with 350gr and 400gr gas checked cast bullets.

Von Gruff who posts here, developed this AR2209 1800-1900 fps MV very accurate load for his 404 and 350gr cast bullet. He also uses AR2208 for full velocity cast bullet loads in his 404. I followed his lead and found the same good performance with his 350gr cast and my own 400gr cast using AR2209. I use one wool wad over the powder charge and I don't think VG uses wads or fillers. I also use a magnum primer just to ensure a good ignition.

Have encountered no problems with this lower load of slower powder.