Bullet alloys, hard cast lead bullets and the foundries.
I have had many discussions with various foundries since the start up of Central Plains Enterprises, LLC. Here is what I now understand about the bullet alloy “lead stream” that the cast bullet is made from. Most of the bullet alloy is derived from the scrap lead market such as wheel weights, roofing lead, linotype, lead pipe. Part of the scrap selected already contains tin and antimony. Both tin and antimony are expensive alloys in their pure form. The mainstay bullet alloy is 2% tin, 6% antimony, 92% lead; this is referred to as 2/6/92 by the foundries and bullet casting handbooks. If this alloy were to be made of virgin metals none of us would be shooting hard cast lead bullets due to the cost.
The foundries are able to select and blend scraps that require a minimum of tin and antimony be added to arrive at the desired alloy for hard cast lead bullets. Scrap lead is extremely important in cost containment of bullet alloys. Linotype, which contains very high amounts of tin and antimony, is becoming rare. Linotype was used in the printing process but modernization has all but eliminated the use of linotype. Wheel weight compounds have less antimony than ten or fifteen years ago, worse than that zinc is showing up in today’s wheel weights. Zinc is undesirable and hard to separate from the desired alloy. Foundries will quit buying wheel weights when the percentage of them made from zinc raises to an undesirable level. Roofing lead and lead pipe are almost pure lead. There is no reliable stream of tin in the scrap market. A good hard cast lead bullet must have tin and antimony. Antimonty hardens the cast bullet and tin makes the alloy flow into the mold. If you look at a pure lead bullet compared to hard cast lead bullets you will see the cast bullet has much sharper lines and shoulders, this is from the tin content.
In a nutshell alloys melt at different temperatures; this is how they can be separated from lead. If you are blending an alloy too high in antimony you can “cook” the antimony off; it will float on top of lead at high temperatures. This process will also remove tin and everything else too. What this means to us is if we order a non standard alloy that has less tin and antimony there may be no cost savings. In fact a 20:1 or 30:1 (lead:tin) alloy will actually cost more to make; it requires the addition of pure tin to pure lead. If the lead portion is derived from scrap any antimony has to be removed from it before the tin can be added. If you see alloys that are not 2/6/92, chances are the caster is “cutting” it with scrap or pure lead, either would be cheaper than a foundry blended alloy.
For an in depth explanation of alloys you can refer to manuals such as the Lyman Cast Bullet Handbook. Even if you don’t plan on going into bullet casting yourself this book is a wealth of information on cast lead bullets and alloys. Being written by Lyman assures that the information presented is factual. It is a great reference book to add to your collection of loading manuals.