50-90 Sharp's duplex load

What would be a couple of suitable smokeless powder choices be, to use in a duplex load in the 50-90 Sharp's. I want to try a duplex load in my 50-90 using around 70 to 80 grains of 2f Swiss and a 550 grain slug. My intent with the duplex load is to reduce fouling and to reduce the load a bit to see how accuracy might improve. Thanks