Firearm slugs formed from a non-toxic lead substitute that includes tungsten. In some embodiments, the firearm slug is formed with a recessed back portion, thus shifting an increased percentage of the slug's net mass toward the front of the slug. In some embodiments, the firearm slug is formed with a recessed front portion. In some embodiments, the slug is a component of a slug cartridge that includes a slug cup. The slug must have a density that is less than, equal to, or greater than lead, or a lead-antimony alloy used for firearm projectiles. In some embodiments, the slug is formed via powder metallurgy from a powder that includes at least one tungsten-containing component and at least one binder. In some embodiments, the slug is cast or otherwise formed from a molten feedstock that includes at least one tungsten-containing component. In some embodiments, the slug is frangible.