I can't comment on loading hard lead balls, or anything about them, as I have never used them. But I can state that they are not needed for taking large animals, such as elk. I've killed plenty of elk with roundballs, and so have my kids, and we've always used pure soft lead. Most broadside shots go completely through the animal, and that includes big bulls.
I offer this experience because I hear a lot of hunters ask about penetration. Usually it goes something like this, "I'm going elk hunting this fall for the first time, so I assume I need to add tin to my pot to make harder balls for proper penetration". One cow elk I killed was quartering away, I hit her just in front of the rear leg and the .54 ball ended up in her chest. That's like 30+ inches of penetration with a pure lead ball.
Just throwing it out there, in case your question pertains to hunting large animals. Bill