Depleted uranium bullets are projectiles made of uranium that has undergone a classified process to make it extremely dense and increase its armor penetration through kinetic energy. Such bullets remain very deadly after they have struck armor by being pyrophoric.
Typical steel rounds shatter upon hitting a very heavily armored target. Depleted uranium burns into vapor when it impacts armor, keeping the round extremely sharp and allowing it to penetrate very thick armor. This also gives it the characteristic of spraying molten metal and white-hot gases once it has penetrated the armor. Depleted uranium is also extremely cheap to manufacture, making it a viable weapon on the battlefield.