This problem can be traced back to World War II. During World War II, there were many heavy industry bases in European countries, so it was very convenient to mine and smelt brass. Coupled with the accumulation during World War I, bullets and shells flooded. During World War II, the United States stored the largest amount of brass, followed by Germany and the third was the Soviet Union. Brass is indispensable to support a huge military force, so all countries pay special attention to it. After a battle, the consumption of copper is far greater than that of petroleum drugs. Although the cartridge case can be recycled, the assembled ammunition is not as fit as the newly cast ammunition, and its lethality will be greatly reduced, so all countries choose to remelt it. Brass is used in ammunition because of its high ductility and solubility, and the bullet is not easy to jam and explode when it leaves the chamber, so it has high precision. China's ammunition is made of steel, because the Japanese army plundered our resources during the war of aggression against China in World War II, resulting in insufficient brass reserves but unwilling to import it. At present, steel ammunition is still used in China, but a thin layer of brass is plated on the periphery of ammunition, which not only improves the efficiency of weapon use but also reduces the cost. Of course, American bullets are pure copper, because the storage capacity is too large to use up. ...

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