Yes, normally water lead pipe is pure lead. I have some and have cast a lot of roundball and conical bullets out of it. As for what mold to get, will be determined by the rifle you shoot, or want to shoot. I see from your list you have a Lyman Great Plains Rifle in .54 caliber. So I would get a LEE .530 or .535 double cavity roundball mold. My GPR shoots both of them very well. So you would be set. Get as much of that lead as they will give you. It will surprise you how fast it disappears.