OK Here is some good info for you.
These are some basics for pouring ball for a muzzleloader, most everything is the same. For weights you don't have to worry about the same quality as for shooting.
This is kind of looong,
but it has a lot of very good info in it for anyone interested in casting.
First, we need to find a source of cheap lead. Telephone company workers, plumbers who work in areas with old homes in them, and scrap metal dealers are good places to look for cheap lead. When you find some, buy a couple of hundred pounds and find a home for it in the garage. It'll come in handy some day. You'll need a way to cut your lead up before melting it down, so unless you can think of a good method (hatchet, hacksaw, etc.), try to find lead that is easily cut, like sheet lead. Don't get overly compulsive about the softness of your lead. I use the old thumbnaiil test when I'm buying lead. If I can make a mark in the lead with my thumbnail, it's soft enough for me. Mind you, you can dig your thumbnail into some pretty hard lead if you put your mind to it, but harder lead makes for a useful hunting projectile anyway.
When you've found a source of cheap lead, bought some and brought it home, clean it thoroughly. There's enough in the way of impurities in lead so that you don't want to have to deal with some of the stinky crud that will come off old plumbers lead. Get the crud off before getting started. A stiff brush will come in handy here.
When you've found your lead, cleaned it, and cut it up in small enough pieces to deal with, you're ready to cast. Take note here that if your pieces are still fairly large, it would be a good idea to buy yourself an "ingot mould" and melt your lead down in either a large melter, or in a simple pot set upon a hot fire. Put your lead in your melter or your pot, and ladle it out into your ingot mould. (Lyman makes good ingot moulds.) You can see four lead, one pound (each) ingots I made in the photograph above.
In order to get started with casting, you'll need an easy to handle melting pot. You can use a larger electric, ten pound melter that pours from the bottom such as the Lee Production Pot IV, which has four inches of clearance between the spigot and the base. That's what I've been using these days. A simple, electric, four pound sinker pot works too. I used one of these for many years. In absence of either, a small pot that you can leave on a hot fire long enough to melt lead will also work. You will need a ladle if you chose to melt your lead this way and you will ladle the molten lead from the pot into your bullet mould. An electric pot is easier and they're cheap to buy.
I set my "melting pot" in a metal tray, which is set within another metal tray. Both trays have rims so that in the event of a spill, the hot lead isn't going anywhere. Set the outside tray upon a small table that is comfortable to work from and set yourself in a comfortable chair in front of that table. Turn the heating element in the pot on and melt some lead. Melting a pot of lead will take a little while. If your melting pot has a temperature gauge, let the lead get hot, but not very hot. As you begin to cast you will learn to approximate the proper temperature. In the beginning, just try setting your temperature gauge in the middle.
When the lead is properly melted, you will need to "flux" a bit. I use bees wax for flux. Other fluxing agents can be purchased in any good gun store. Fluxing will help purify your lead.
In order to flux, when your lead is melted, drop in a bit of fluxing agent. Use an old spoon to stir the flux into the melted lead. When the mixture has been well stirred, spoon whatever crud floats to the top of the lead off and throw it away. You are now ready to cast.
Fluxing: Why fluxing is necessary, what effect it has on the alloy, and how to do it.
Clean metal casts most easily and well. Fluxing is the process whereby we clean our molten metal. The 'dross' (slag and other contaminants) is in part oxides of the metal, and unoxidized metal in the form of very small spheres (shot). The 'shotted metal' is held in that form by a thin layer of oxides and contaminants, the surface tension of the oxide layer prevents the shotted metal from being wetted by the molten metal. The purpose of the flux is to break down the surface tension, and allow the molten metal inside the shot to return to the main body of the metal. The loosened oxides appear to be coagulated by the flux and suspended in the flux body. This can then be skimmed off. This is the only effect that fluxing the molten alloy has. The only way fluxing can change the alloy is by returning shotted metals to the general mix. Generally, this will have little effect on the alloy's composition. Most of the dross will be in very small particles distributed throughout the pot. The flux acts almost entirely on the surface though-which is why it is necessary to stir the metal thoroughly when fluxing.
Once the lead is melted, drop in a pea sized piece of wax or the appropriate amount (per instructions) of a commercial flux. If it smokes, light the smoke with a match. Stir the lead, being sure to scrape the sides and bottom of the pot. After a bit, a bunch of brown junk will rise to the top of the molten lead. This is the dross -use your mixing spoon to remove it and place it in a safe container. Repeat the cycle two or three times.
It is fairly common to toss the dross removed when fluxing into a coffee can. KEEP THAT STUFF DRY. Under the right conditions, certain contaminants in the dross can release stibine gas, which is toxic. Recently, I have gone to using a NEW 1 gallon paint can. Cost two bucks at a paint store, but now I have no excuse to forget to cover the dross can. I figure the can will hold several years of dross at the current rate I am generating it.
Pick up the mould and pour some of the molten lead through the small hole in the top with the "spru cutter" of the mould in place.
Hold the mould handles together for a few seconds and use a "knocking stick", like the one pictured, to push the spru cutter off the top of the mould. Hold the mould over a small piece of cardboard, like the small cardboard box in the picture, and open the handles of the mould. If the ball does not immediately drop out, use your knocking stick to push the ball out. For this purpose it is a good idea to drive a nail through one end of your knocking stick so that you can use the nail tip to push the ball out of the mould.
Don't expect the first dozen or so balls you cast in a cold mould to come out perfect. Throw them back into the melting pot until balls do begin to come out perfect. If this isn't happening in a reasonable length of time, adjust the temperature of the melting pot.
Notice the wrinkles? It may take a bunch of casts to get the mold heated up enough to cast good balls. Once you get a good ball, you should be OK. If the mold gets too hot, the balls will come out with a frosted surface. Let the mold cool, I usually just set it on a concrete floor for a few minutes.
Lead: Lead selection depends on your desired purpose. Like most folks who cast ball for their ML guns, I salvage lead. I guess the difference is that I had a commercial bullet casting firm at a time when I had access to a metallurgical lab. I had some tests done on the most common alloys available as scrap. Casting at home, there are a few problems we all commonly encounter, and a few misconceptions that create further problems. What is often considered as 'pure' lead isn't, and what is considered as 'unusable' for our purposes often actually is.
Test 1: Clip-on wheelweights. These are the ones everyone thinks of as 'hard'.
Trace elements 1.9% (Cadmium, calcium, silver, copper, etc)
Test 2: Adhesive wheelweights. These come in strips, and are stuck onto mag wheels.
Trace elements 1.75% (Arsenic, cadmium, calcium, copper, silver, tin, etc).
Test 3: Plumber's lead (caulking lead). The stuff usually recommended for ML use. Bought from a local plumber in factory ingots.
Trace elements 1.4% (Cadmium, calcium, copper, silver, tin)
Test 4: Salvage lead (from houses built about 1930-1950). Lead flashing, caulking, pipe, shower and tub liners, etc.
Trace elements 1.8% (The usual stuff).
As a test, I also had a test run on 'pure' lead from a chemical supply house. It came back as lead 99.8% lead.
The dead-soft lead used for pipes, caulking, etc, that is so nice and soft when found in the junk yard was extruded, not cast. One source said tin and antimony were controlled to give more desired characteristics in the extrusion process. When lead is extruded (or swaged, as in sizing a cast bullet or swaging a ball) it softens. It pays to be aware of this when scrounging for lead.
I really can't see any difference between the salvaged adhesive WW, the plumbers lead, and the salvaged lead pipe for use in a muzzle loader or cap and ball revolver.. Cost is a major factor. The WW runs (locally) about 10 cents/pound. The salvaged plumbers lead runs about 13 cents/pound at a local salvage yard. The lead from the plumber was around a buck a pound.
There is no safe way that a person at home can remove tin, antimony, etc from lead. Once it is alloyed, it requires a refinery to remove. By actual test (using an alloy that started as 95% lead, 2.5% antimony, .5% tin, .1% arsenic, and 1.9% trace elements), after 12 hours at 850 degrees F skimming every 20-30 minutes (about 30 times), the alloy was 95.21% lead, 2.51% antimony, .31% tin, .07% arsenic, 1.9% trace elements.
(Safety warning: By its nature, casting bullets exposes the caster to some risk. You will be working with potentially toxic materials at temps high enough to cause severe burns. Protection from lead poisoning is generally simple. You should have good ventilation. Wash your hands after handling lead. Don't eat, drink, or smoke while casting. Wash the clothes worn while casting immediately after casting, separately from other clothing. Cast in an area protected from rain. Don't let sweat, etc., fall into the molten lead. Both will result in an explosion of lead. Be prepared to apply first aid to any burns.)
DO NOT USE AN ALUMINUM PAN TO MELT LEAD. THE MELTING POINT OF ALUMINUM IS CLOSE ENOUGH TO THAT OF LEAD THAT THE BOTTOM MAY DROP OUT OF THE PAN.