Consider 300 grain bullets . Any thing heavier increases recoil to an UNPLEASANT level. Hornady,Remington and several others make them. varget ,H4895,h4198 and many other powders are fine in the 45-70. Using cast in the compensated barrel MIGHT cause a leading condition that is hard to remove. that depends on the type of compensator. I've used 2400 and Unique powder in mine with no problem. I have a ported barrel and found cast bullets foul the ports rather quickly. Hornady 350 grain bullets are much harder than needed for thin skinned deer. They would be Okay for targets though, depending on accuracy!