Who and when did anyone criminalize any of those metals?
Don't the shotshells for waterfowling use tungsten shot?
If some kind of steel projectiles are used, unless it's of a very soft variety, isn't it going to wear out the rifling fairly quickly?
>>Don't the shotshells for waterfowling use tungsten shot?
Yes, but liberty isn't secured with shotguns, as a rule.
>>If some kind of steel projectiles are used, unless it's of a very soft variety, isn't it going to wear out the rifling fairly quickly?
Copper jacketing helps a lot.
Handgun ammo with non-lead alloys are usually called "cop-killer" and are banned under federal law. Steel, bronze, tungsten, moly (core), etc... it's all banned.