Bullets can be made from copper but there’s almost no reasonable substitute for lead shot, anything else close to being as dense is expensive. That is, bullets for center-fire weapons can be made from copper, but a 22 might not really have the power to move copper bullets across rifling and most rimfire weapons could not easily be cleaned for copper fouling. Such a law might spell the end of the 22 and other new rimfire calibers.
That is, you’re probably talking about getting rid of shotguns and 22s.