When lead shot was banned for waterfowl hunting more than 30 years ago, steel was the only workable nontoxic pellet material available. Early steel loads weren't very good, but ammo makers soon began improving them by using better wads, waterproofing, and more consistent, cleaner-burning powders. Steel became an effective, affordable shot material, but its lower density means it will never have the same downrange energy as lead. So ammo makers started searching for alternatives, including experimental loads of copper and tin. The best candidates turned out to be bismuth and tungsten, which are being used to manufacture some of today's best-performing loads.
Originally promoted in the 1990s by publishing magnate Robert Petersen, bismuth shot is made from a bismuth-tin alloy. The pellets have a density of 9.6 grams per cubic centimeter (g/cc), about halfway between lead (11.2) and steel (7.8). Bismuth is quite soft and brittle and, unlike steel, won't damage barrels in older guns. The downside is that some of those brittle pellets can be crushed and broken upon ignition, reducing pattern efficiency.
Bismuth faded from the market for a while following Petersen's death in 2007, but it's back now, manufactured by a growing number of companies including Fiocchi, Remington, Hevi-Shot, Federal, Kent, Rio, Winchester, and Boss. While they all work, a couple of brands stand out. To keep prices as low as $1.50 per shell, Boss sells only direct to consumer. Their copper-plated pellets are less prone to shattering and deformation, and as a result, they pattern better than most other brands. Winchester's new buffered bismuth loads go a step further to protect pellets, cushioning each one in a microbead buffer material that virtually eliminates pellet breakage.
Patterns from bismuth loads tend to be more open than steel, so you should use a tighter choke. The increased density of bismuth also means that you can shoot one or two pellet sizes smaller than you can with steel. If you shoot steel 2s, for example, choose bismuth 3s or 4s.
A very hard, dense, expensive metal, tungsten has been made into pellets by combining it with nickel and iron to varying degrees of density and by blending powdered tungsten with polymer. In the 1990s, Federal Cartridge Company first introduced a tungsten-iron alloy shot that was almost as dense as lead. Federal and Kent both offered tungsten-polymer loads that were soft and suitable for older shotguns. Kent's shells, branded as Tungsten-Matrix, are still available. They perform like lead but cost about $4 per shell.
The breakthrough for tungsten came in 1998, when Darryl Amick, the metallurgist who developed Federal's tungsten-iron pellets, found a partner who agreed to back him financially on the condition that Amick would develop pellets that were denser than lead. The result was 12 g/cc Hevi-Shot, which patterns as tightly as steel and hits harder than lead. Like steel, it is not suitable for use in older shotguns. Tungsten-iron shotshells have been loaded to several different densities, some of which are much denser than lead, like Federal's Heavyweight Tungsten Super Shot (TSS) at 18 g/cc.
Tungsten creates tight patterns, and its density allows you to shoot smaller pellets. Choose a more open choke and shot that is two or three sizes smaller than you would opt for with steel. Hevi-Shot 4s are a great all-around duck and goose load. If you're shooting TSS, you can use shot as small as 9 for ducks and 7 for geese. Because TSS also patterns quite tightly, you will want to pattern-test your gun with improved cylinder or light modified chokes.
The high price of tungsten and bismuth ammunition led to the development of blended loads. Both Federal and Apex offer blended steel/TSS loads, while Hevi-Shot and Browning make steel/bismuth loads. These shotshells combine a smaller premium pellet with a larger steel pellet with a similar velocity. Because they use fewer of the expensive pellets, they can sell for less. Blended loads perform best at midrange distances within the effective range of the steel pellets. The smaller, denser premium pellets add density and energy to the pattern.