Mark,
Here is some information gleaned from reading articles on fishing equipment. I would suspect shotgun pellets would be the equivalent of very small fishing jigs in manufacturing terms.
Tungsten fishing weights are not machined, nor are they melted and poured in a mold.
Unfortunately, the method of manufacture is beyond most individuals and home-businesses. Tungsten fishing weights (and virtually all other tungsten parts, rod, or plate used in manufacturing) are made by a process called 'compression forming.' Tungsten powder is poured into a die that is the desired shape of the finished product, and then using a hydraulically-powered ram or punch, the powder is compressed under enormous weight until the powder becomes one solid piece. The solid part is then ejected from the die, and carefully set aside.
What you have then, is a tungsten fishing weight that is about as hard and strong as an aspirin tablet. To make it strong enough to be used, it needs to be 'sintered.' Sintering involves heating the tungsten part in a furnace until the compressed powder just barely starts to melt, which essentially solidifies the part, and makes it strong.
Now, since tungsten's melting point is so unreasonably high, the tungsten powder used for compression forming has to be mixed with another metal that will melt during sintering. This is usually a few percent of copper, nickel, or iron, but other metals like tin are sometimes used. The small amount of copper powder (or other metal) in the mix is what actually (just barely) melts, and binds all the particles together. For some applications, the compressed tungsten powder/metal mix is so strong after compession, that it doesn't need to be sintered. Also, tungsten powder is very hard, so it tends to clump together and won't flow through the machinery very well and scratches the dies, and the addition of the copper/nickel/etc makes it less abrasive. Often a tiny amount of stearate or a special wax is added so the metal powder is easier to handle, and flows into the dies easier. If the part is going to be machined after sintering, the addition of copper and nickel make it MUCH easier to machine with cutting tools-- pure or nearly pure tungsten is very hard to work. Even very large slabs or or rods of tungsten for industrial/military use are made by the compression-forming process, and sintered.
[strike][/strike]
