OK Friar Tuck, you may not have wanted to start an argument, but you probably did. First, you didn't say what you want to do with your cast balls. Hunt, plink, shoot targets in competition, make fishing weights? Since you posted in the Roundball Accuracy category, I'll try to help you with accuracy, rather than penetration into the vitals of an elephant.
There's no law or rule, that I'm aware of, that says you have to use pure lead for your round ball casting. But, there are some things you need to be aware of. Most of them are just common sense. Do stay away from battery plates and other really nasty sources of lead.
Here's a few characteristics of pure lead.
1. It melts at a lower temperature than most other suitable metals
2. It weighs more per volume than most other suitable metals (You probably could use pure gold.)
3. It's softer than most alloys.
Lead and lead alloy hardness is rated on a scale known as the Brinell scale. Similarly, steel alloys are rated on the Rockwell scale.
Pure lead has a Brinell hardness of about 5; wheel weights have a brinell hardness of about 8 or 9. Linotype has a brinell hardness of about 22.
You can buy a rather inexpensive tester to let you know how hard your scrap lead may be. Lead can be dented pretty easily with a fingernail.
For the pressures that we deal with in a muzzleloader, pure lead "obturates" better than does a harder metal. Yes the cloth patch initally holds the ball in place, but as the powder charge burns and pressure builds, the back end of the ball gets a "kick in the pants and initally travels faster than the front of the ball. Then the ball expands in diameter and begins to fill out the bore. At that point, the patch plays a much smaller role. If the ball is pure lead, it obturates more quickly and completely than does a ball made from some harder alloy. Better obturation = better accuracy.
So, if you're using an alloy, you'll need to use a greater powder charge to get the desired "flattening" and bore filling effect.
For maximum accuracy, you need to use heavy enough charges to at least have the ball obturate. If you're using an 8 bore and going after elephant, use about 250 grains of 2f behind a hardened ball. You'll have accuracy and plenty of penetration too.
High power rifles and pistols operate at higher pressure and actually do better with harder alloys. They also need alloys to reduce leading.
Some people don't really care because whatever scrap they can find is good enough. They'll probably use an old pair of jeans or the tail of their shirt for a patch too and be happy as a pig in mud. If accuracy isn't a concern, heck, use old steel ball bearings. The first muzzleloader that I made used firecrackers and marbles shot out of a piece of pipe.
So, if you understand the principles involved, you'll know what to do when you're ready to squeeze a little bit more accuracy out of your muzzleloader. You're going to have a great time. The more you experiment and make things with your own hands, the more fun you're going to have.
