I agree, that is a stiff load for a cast bullet. You can push cast to high velocities, but you have to be careful with bullet hardness if you get upwards of 2000 fps. It sounds like you've sized your bullet correctly. I've had excellent success with 19.0 gr of SR4759 under the Lee 185 gr bullet cast from WW. It gives me about 1700 fps out of my cut-down 24" barrel. Unless you want to spend a lot of time experimenting, keep your cast bullet velocities under 1800 fps. As mentioned above, an excellent all-round load in just about any .30-cal round is 16 gr of 2400. I think the 19-20 gr of 4759 approximates this load. Your best cast bullet powders will be SR4759, 2400 and 5744. If this is your first try at cast bullets, don't try to match jacketed bullet velocity. If you don't already have it, purchase the Lyman Cast Bullet handbook.