If you cut a jacketed bullet open or shoot one into wet sand it's a copper steel coated jacket. There's no way that a soft copper jacket is going to wear out a hardened steel barrel. I did a lot of wet sand ballastics testing and found out every copper coated bullet has a thin steel jacket.

Now I use moly coated leadcast bullets. I do not wash the moly out of the barrel. I run some full power jacketed bullets at the end of the shoot just to keep the feel of the full power loads. The moly eliminates wear of the forcing cone and barrel.