Can or may?
You could copper clad just about any metal and fire it. Legally? It gets tricky and I am not fully familiar with the law, I’m pretty sure steel and bronze were made illegal, never mind I’ll just google it....
“Armor-piercing ammunition, sometimes referred to as metal-piercing ammunition, is ammunition that is designed primarily to penetrate metal or armor, including body armor commonly worn by police officers. Under federal law, armor-piercing ammunition is defined as any projectile or projectile core that may be used in a handgun and that is constructed entirely from one or a combination of tungsten alloys, steel, iron, brass, bronze, beryllium copper, or depleted uranium.15 In addition, armor-piercing ammunition is defined as a full jacketed projectile “larger than .22 caliber designed and intended for use in a handgun and whose jacket has a weight of more than 25 percent of the total weight of the projectile.” Id. The Attorney General is required to furnish information to each licensed dealer defining which projectiles are considered armor-piercing ammunition as defined in 18 U.S.C. § 921(a)(17)(B).16”
Now that certainly cleared things up. :(
Notice it only applies to handguns.