Your alloy choice has more impact on cast bullet performance than almost any other variable. The right alloy produces well-filled bullets that fly accurately and don't lead your barrel. The wrong alloy causes leading, poor accuracy, and frustration. This guide covers every major bullet casting alloy, its hardness, best uses, and where to get it.
Bullet hardness is measured on the Brinell Hardness Number scale (BHN). Pure lead is approximately 5 BHN — very soft. Adding antimony increases hardness; tin improves castability and fill. The general rule: higher velocity requires harder alloy to prevent leading and gas cutting.
| Alloy | Composition | BHN | Best For |
|---|---|---|---|
| Pure lead | 100% Pb | 5 | Black powder, very low velocity |
| 1:20 tin/lead | 5% Sn, 95% Pb | 6–7 | Low velocity pistol, .38 Special target |
| Wheel weight (WW) | Pb, ~2% Sb, ~0.5% Sn | 9–12 | Most pistol cartridges under 1,200 fps |
| Lyman #2 | 90% Pb, 5% Sn, 5% Sb | 15 | Pistol and mid-range rifle, 1,200–1,500 fps |
| Heat-treated WW | Same as WW, quenched | 18–22 | Rifle and high-velocity pistol |
| Linotype | 84% Pb, 12% Sb, 4% Sn | 22 | High-velocity rifle, .30 caliber |
| Monotype | 76% Pb, 17% Sb, 7% Sn | 26+ | Maximum hardness applications |
For most hobbyist casters, wheel weights are the backbone of their alloy supply. They're widely available from tire shops (often free or cheap), cast well, and have adequate hardness for the majority of pistol applications. The antimony content (around 2%) provides meaningful hardness over pure lead without making the alloy brittle.
One important caveat: wheel weights have changed. Older steel clip-on weights are ideal casting alloy. Modern adhesive weights are often zinc or other metals that are not suitable for casting — and zinc contamination ruins a batch of alloy. Sort your wheel weights carefully and discard any that don't look like traditional lead-colored clip-on weights.
The zinc test: Zinc wheel weights float in molten lead while lead weights sink. Keep your furnace temperature below 800°F when melting wheel weights — zinc melts at 787°F but won't contaminate your melt at lower temperatures, making it easy to fish out before it dissolves.
Lyman #2 is a time-tested alloy formula — 90% lead, 5% tin, 5% antimony — that balances hardness, castability, and cost. The higher tin content versus wheel weights produces excellent mold fill, sharp edges on flat-nosed designs, and a bright surface finish. At 15 BHN it handles most pistol applications and moderate rifle loads comfortably. Many serious casters consider Lyman #2 the gold standard for general-purpose bullet casting.
One of the most cost-effective ways to get hard alloy is heat treating standard wheel weight alloy. The process is straightforward: cast your bullets, then heat them in an oven to 450°F for one hour, and quench them immediately in cold water. This raises wheel weight BHN from around 10–12 up to 18–22 — hard enough for most rifle applications.
Heat treating adds a step but dramatically extends the velocity range of cheap, widely available wheel weight alloy. Many high-volume rifle casters use heat-treated wheel weights exclusively rather than paying for linotype.
Linotype was originally used in printing presses and contains approximately 84% lead, 12% antimony, and 4% tin. At 22 BHN it's the hardest commonly available alloy short of specialty products. It's the traditional choice for high-velocity cast rifle bullets and produces excellent results in .30 caliber and larger rifle cartridges at velocities up to 2,000 fps with gas checks.
Linotype is harder to source than wheel weights — printing presses are largely obsolete — but it's available from specialty casting suppliers and sometimes surplus dealers. Expect to pay more per pound than wheel weights.
| Application | Velocity Range | Recommended Alloy |
|---|---|---|
| Black powder pistol | Under 800 fps | Pure lead or 1:20 |
| Cowboy action / .38 Spl target | 700–900 fps | Wheel weight or softer |
| Standard pistol (9mm, .45 ACP) | 850–1,100 fps | Wheel weight |
| Hot pistol (.357, 10mm, .44 Mag) | 1,100–1,400 fps | Lyman #2 or harder |
| Rifle reduced loads | 1,400–1,800 fps | Lyman #2 + gas check |
| Rifle standard loads | 1,800–2,200 fps | Heat-treated WW or linotype + gas check |
Whether you're running wheel weights or linotype, the M2R Automatic Casting Machine handles any standard alloy at high volume with consistent results.
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