The Black Powder IMO is a great choice of powder. I know you're going to hear a lot of people recommend BlackHorn 209, but that black powder will do anything that Blackhorn can do for you in the field. Now for the load, remember you have a magnum capable rifle. And while I agree smaller loads work fine. because of the distance you want to shoot, try boosting that powder charge up. Move up to 90 grains of 2f and see if the accuracy is not better. In fact if the accuracy improves, move it up to a little more .. say 100-110 and see if the accuracy is still there. While you might not like the idea of the stronger charges... if the accuracy is there and you have to shoot longer distances, the stronger powder charge will not hurt..