Bullet Casting 101: Alloys

Back in 2015, Ray Davies wrote an excellent guest post on the basics of bullet casting. Since it’s been a while, I’d like to review this topic and go into more detail. 

While detail-oriented, bullet casting isn’t especially complicated, or at least doesn’t have to be. As with reloading, casting bullets may not save us money, but it should allow us to shoot more for the same amount of money spent.

 

Bullet Alloys

Bullets are one of the consumables in ammunition reloading, and are possibly the most expensive after the brass cartridge casing. They are generally made up of either a lead core surrounded by a copper alloy jacket, or unjacketed lead alloy. 

Unless we’re shooting a black powder firearm, we really don’t want pure lead; it’s too soft and at even moderate handgun velocities, the bullets will smear and deposit a coating of lead inside the barrel. The best alloy for bullets is mostly lead with small amounts of tin and antimony added. Arsenic, copper, and silver have also been used in bullet alloys, but tin and antimony are the most common.

The addition of Tin (atomic symbol Sn), between two and five percent, aids primarily in reducing surface tension which improves mold fill-out as the molten metal will more closely follow the contours inside the mold. Antimony (atomic symbol Sb) added in the range of three to six percent is used to improve the hardness of the alloy, which aids in creation of bullets that retain their structural integrity when fired down a barrel.

Wheel Weights
One of the best starting alloys is clip-on lead wheel weights that used to be found in every tire shop and garage in the country. Sadly, many states have banned the use of lead wheel weights and most are now steel or zinc.

Important Note: 

Lead and zinc do not get along! 

Even small amounts of zinc can contaminate the mix, rendering it unusable. 

A box of clean wheel weights.

An easy test is to scratch the weights with a pair of side cutters. If they leave a nice mark with little effort, it’s lead; if they barely scratch the surface, it’s probably zinc or steel. Put them aside, and you might be able to bring them to your local scrap yard.

Clip-on lead wheel weights already have about half a percent of tin and around three percent antimony in their makeup. These can be used as-is in low pressure, low velocity handgun loads such as .45 ACP; however, fill-out and bullet hardness may be less than desired.

More Sources
An excellent source of tin and antimony is pewter -- real pewter, not food-safe pewter found in restaurant supply houses. Pewter is mostly tin with some antimony, and adding a small amount of pewter to lead can greatly improve both fill-out and bullet hardness.

Pewter: a good yard sale find

Another good source of bullet lead is found in range backstops, so ask range management about the possibility of scavenging some lead from the backstop. Many ranges have contracts where the backstop is cleaned every so often; if your range does this, see about getting in touch with the lead removal company. A couple of five gallon buckets of range lead can go a long way.

Important safety note:

Do not ever use lead plates from old car batteries! They can release fatally toxic gasses when melted. Avoid them at all costs.

There are other sources of bullet lead, but I think you get the idea.

References

There are many commercial sources for reloading both jacketed and unjacketed bullets, but one of the best references on bullet casting can be found in Glen Fryxell’s free online book From Ingot to Target (a pdf version may be found here), with second place going to the Lyman Cast Bullet Handbook.

Finally, here’s a downloadable lead alloy calculator which allows you to calculate how much of what metals to add to your alloy for a particular bullet hardness, called the Brinell Scale. It’s a spreadsheet and can be opened in Excel or OpenOffice.