Nosler has data for Accubond and CC in 300gr. I will try 300gr CC and 78gr MRP soon.Using H4350, Hodgdon drops 2 grains off the starting weight, everytime they go up 25 grains in bullets weight. ie; 200gr start at 77, 225gr start at 75, 250gr start at 73, 275 start at 71. So I'd drop down to 65 grains and work up from there with the 300's. But that's just me. I looked everywhere I knew to look, and even Ammoguide dont have any 300gr loads for the 340.