Experiments with Bismuth
Abstract:
Beginning 1 July 2019, the State of California will require the use of lead-free projectiles while taking all game and non-game animals. The availability of lead-free projectiles has been problematic since first requiring their use within the designated Condor range on 1 July 2008. For many older weapons or unusual calibers, California routinely exceed the total national output of lead-free ammunition, causing many to retire firearms or simply leaving the shooting sports altogether.
Those choosing to hunt with traditional muzzleloader using patched round ball were particularly hard hit by this requirement as there was only one approved lead-free round ball on the market. Those balls were manufactured by ITX using a proprietary powdered metal material that were expensive and only offered in 3 sizes.
Recently, RotoMetals of San Leandro CA began marketing a lead-free bullet casting alloy consisting of 88% bismuth and 12% tin that is on CA Department of Fish Wildlife’s approved list. It is primarily marketed towards those who choose to cast their own conical bullets for either hunting or silhouette shooting. Since the product comes in 1 pound bars, it was thought that it would lend itself well for casting round balls for traditional muzzleloaders.
The research presented here investigates the viability of the RotoMetal alloy as a green substitute for hand cast .54 caliber lead round balls while hunting.
Preparation:
In discussion with RotoMetal, it was revealed that the alloy expanded slightly during the post casting cooling, but to what degree was unknown. Because both bismuth and tin have lower densities than lead, the cast round ball was expected to be lighter, but again, to what degree was unknown.
Because of these unknowns a Lee two-cavity .530 bullet mold was chosen in the hopes that the final diameter was equal to or less than .535”.
A new RCBS cast iron metal melting pot was purchased as was a new pour ladle. Three pounds of the alloy was placed in the pot and melted at around 375 F. Pouring commenced when the temperature of the molten metal reached 500 F.
Casting:
Three pounds of the alloy yielded 99 poured balls. A sample population of 25 balls were selected at random, weighed and diameter measured with the following results.
The average/mean bullet diameter was .53394 inches. Maximum diameter was .5355 inches and the minimum .5330 inches.