have done some research for the perfect load for my SS Redhawk 7.5 in 45 colt. I see a 250 grain cast bullet. Over 18.5 grains of 2400 doing 1200 fps. Then I see 20 grains of 2400 hitting 1197 fps. What is up?? Or could some one give a realistic mix for my 1200 fps goals…. Thanks